Polydentate Amidinato-Silylenes, -Germylenes and -Stannylenes.

This review article focuses on amidinatotetrylenes that potentially can (or have already shown to) behave as bi- or tridentate ligands because they contain at least one amidinatotetrylene moiety (silylene, germylene or stannylene) and one (or more) additional coordinable fragment(s). Currently, they are being widely used as ligands in coordination chemistry, small molecule activation and catalysis. This review classifies those that have been isolated as transition metal-free compounds into five families that differ in the position(s) of the donor group(s) (D) on the amidinatotetrylene moiety, namely: ED{R1NC(R2)NR1}, EX{DNC(R2)NR1}, EX{R1NC(D)NR1}, EX{DNC(R2)ND} and E{R1NC(R2)ND}2 (E=Si, Ge or Sn). Those that do not exist as transition metal-free compounds but have been observed as ligands in transition metal complexes are cyclometallated and ring-opened amidinatotetrylene ligands. This article presents schematic descriptions of their structures, the approaches used for their syntheses and a quick overview of their involvement (as ligands) in transition metal-catalysed reactions. The literature is covered up to the end of 2023.

Amidinatotetrylenes Donor Functionalized on Both N Atoms: Structures and Coordination Chemistry.

E(hmds)(bqfam) (E = Ge (1a), Sn (1b); hmds = N(SiMe3)2, bqfam = N,N'-bis(quinol-8-yl)formamidinate), which are amidinatotetrylenes equipped with quinol-8-yl fragments on the amidinate N atoms, have been synthesized from the formamidine Hbqfam and Ge(hmds)2 or SnCl(hmds). Both 1a and 1b are fluxional in solution at room temperature, as the E atom oscillates from being attached to the two amidinate N atoms to being chelated by an amidinate N atom and its closest quinolyl N atom (both situations are similarly stable according to density functional theory calculations). The hmds group of 1a and 1b is still reactive and the deprotonation of another equivalent of Hbqfam can be achieved, allowing the formation of the homoleptic derivatives E(bqfam)2 (E = Ge, Sn). The reactions of 1a and 1b with [AuCl(tht)] (tht = tetrahydrothiophene), [PdCl2(MeCN)2], [PtCl2(cod)] (cod = cycloocta-1,5-diene), [Ru3(CO)12] and [Co2(CO)8] have been investigated. The gold(I) complexes [AuCl{κE-E(hmds)(bqfam)}] (E = Ge, Sn) have a monodentate κE-tetrylene ligand and display fluxional behavior in solution the same as that of 1a and 1b. However, the palladium(II) and platinum(II) complexes [MCl{κ3E,N,N'-ECl(hmds)(bqfam)}] (M = Pd, Pt; E = Ge, Sn) contain a κ3E,N,N'-chloridotetryl ligand that arises from the insertion of the tetrylene E atom into an M-Cl bond and the coordination of an amidinate N atom and its closest quinolyl N atom to the metal center. Finally, the binuclear ruthenium(0) and cobalt(0) complexes [Ru2{µE-κ3E,N,N'-E(hmds)(bqfam)}(CO)6] and [Co2{µE-κ3E,N,N'-E(hmds)(bqfam)}(µ-CO)(CO)4] (E = Ge, Sn) have a related κ3E,N,N'-tetrylene ligand that bridges two metal atoms through the E atom. For the κ3E,N,N'-metal complexes, the quinolyl fragment not attached to the metal is pendant in all the germanium compounds but, for the tin derivatives, is attached to (in the Pd and Pt complexes) or may interact with (in the Ru2 and Co2 complexes) the tin atom.

Attaching Metal-Containing Moieties to ß-Lactam Antibiotics: The Case of Penicillin and Cephalosporin.

Procedures for the preparation of transition metal complexes having intact bicyclic cepham or penam systems as ligands have been developed. Starting from readily available 4-azido-2-azetidinones, a synthetic approach has been tuned using a copper-catalyzed azide-alkyne cycloaddition between 3-azido-2-azetinones and alkynes, followed by methylation and transmetalation to Au(I) and Ir(III) complexes from the mesoionic carbene Ag(I) complexes. This methodology was applied to 6-azido penam and 7-azido cepham derivatives to build 6-(1,2,3-triazolyl)penam and 7-(1,2,3-triazolyl)cepham proligands, which upon methylation and metalation with Au(I) and Ir(III) complexes yielded products derived from the coordination of the metal to the penam C6 and cepham C7 positions, preserving intact the bicyclic structure of the penicillin and cephalosporin scaffolds. The crystal structure of complex 28b, which has an Ir atom directly bonded to the intact penicillin bicycle, was determined by X-ray diffraction. This is the first structural report of a penicillin-transition-metal complex having the bicyclic system of these antibiotics intact. The selectivity of the coordination processes was interpreted using DFT calculations.

Tetrelanes versus Tetrylenes as Precursors to Transition Metal Complexes Featuring Tridentate PEP Tetryl Ligands (E=Si, Ge, Sn).

Two synthetic approaches have until now been used to synthesize transition metal complexes having a tridentate (pincer or tripod) PEP tetryl (E=Si, Ge, Sn) ligand. These approaches differ in the metal-free precursor, tetrelane or tetrylene, that gives rise to the corresponding PEP tetryl ligand. Tetrelanes (PSiP silanes, PGeP germanes and PSnP stannanes and simple phosphane-free stannanes) have led to tetryl ligands by oxidatively adding an E-X bond (X=H, C or halogen in most cases) to the metal atom of a low-valent transition metal complex, whereas tetrylenes (PGeP germylenes and PSnP stannylenes) have led to tetryl ligands upon insertion of their E atom into an M-X bond (X=Cl in most cases) of the metal precursor or through a derivatization of the E atom after the tetrylene fragment is coordinated to the metal. For each synthetic approach, all the currently known types of PEP tetryl ligand frameworks that have been found in transition metal complexes are presented and discussed in this review.

Synthesis and Some Coordination Chemistry of Phosphane-Difunctionalized Bis(amidinato)-Heavier Tetrylenes: A Previously Unknown Class of PEP Tetrylenes (E = Ge and Sn).

The bis(amidinato)-heavier tetrylenes E(bzamP)2 (E = Ge (2a) and Sn (2b); bzamP = N-isopropyl-N'-(diphenylphosphanylethyl)benzamidinate), which are equipped with one heavier tetrylene (germylene or stannylene) and two phosphane fragments (one on each amidinate moiety) as coordinable groups, have been synthesized from the benzamidinum salt [H2bzamP]Cl and GeCl2(dioxane) or SnCl2 in 2:1 mol ratio. A preliminary inspection of their coordination chemistry has shown that their amidinate group can also be involved in the bonding with the metal atoms as tridentate ENP and tetradentate PENP' coordination modes have been observed for the ECl(bzamP)2 ligand of [Ir{κ3E,N,P-ECl(bzamP)2}(cod)] (E = Ge (3a) and Sn (3b); cod = η4-1,5-cyclooctadiene) and the E(bzamP)2 ligand of [Ni{κ4E,N,P,P'-E(bzamP)2}] (E = Ge (4a) and Sn (4b)), which are products of reactions of 2a and 2b with [IrCl(cod)]2 (1:0.5 mol ratio) and [Ni(cod)2] (1:1 mol ratio), respectively. These products contain a 5-membered NCNEM ring that results from the insertion of the metal M atom into an E-N bond of 2a and 2b. Additionally, while iridium(I) complexes 3a and 3b are chloridotetryl derivatives (insertion of the tetrylene E atom into the Ir-Cl bond has also occurred) that have an uncoordinated phosphane group, nickel(0) complexes 4a and 4b contain a tetrylene fragment that, maintaining the lone pair, behaves as a σ-acceptor (Z-type) ligand.

Synthesis, Structure, and Photophysical Properties of Platinum(II) (N,C,N') Pincer Complexes Derived from Purine Nucleobases†.

The synthesis of a series of Pt{κ3-N,C,N'-[L]}X (X = Cl, RC≡C) pincer complexes derived from purine and purine nucleosides is reported. In these complexes, the 6-phenylpurine skeleton provides the N,C-cyclometalated fragment, whereas an amine, imine, or pyridine substituent of the phenyl ring supplies the additional N'-coordination point to the pincer complex. The purine N,C-fragment has two coordination positions with the metal (N1 and N7), but the formation of the platinum complexes is totally regioselective. Coordination through the N7 position leads to the thermodynamically favored [6.5]-Pt{κ3-N7,C,N'-[L]}X complexes. However, the coordination through the N1 position is preferred by the amino derivatives, leading to the isomeric kinetic [5.5]-Pt{κ3-N1,C,N'-[L]}X complexes. Extension of the reported methodology to complexes having both pincer and acetylide ligands derived from nucleosides allows the preparation of novel heteroleptic bis-nucleoside compounds that could be regarded as organometallic models of Pt-induced interstrand cross-link. Complexes having amine or pyridine arms are green phosphorescence emitters upon photoexcitation at low concentrations in CH2Cl2 solution and in poly(methyl methacrylate) (PMMA) films. They undergo self-quenching at high concentrations due to molecular aggregation. The presence of intermolecular π-π stacking and weak Pt···Pt interactions was also observed in the solid state by X-ray diffraction analysis.

Dipyrromethane-Based PGeP Pincer Germyl Rhodium Complexes.

A family of germyl rhodium complexes derived from the PGeP germylene 2,2'-bis(di-isopropylphosphanylmethyl)-5,5'-dimethyldipyrromethane-1,1'-diylgermanium(II), Ge(pyrmPi Pr2 )2 CMe2 (1), has been prepared. Germylene 1 reacted readily with [RhCl(PPh3 )3 ] and [RhCl(cod)(PPh3 )] (cod=1,5-cyclooctadiene) to give, in both cases, the PGeP-pincer chloridogermyl rhodium(I) derivative [Rh{κ3 P,Ge,P-GeCl(pyrmPi Pr2 )2 CMe2 }(PPh3 )] (2). Similarly, the reaction of 1 with [RhCl(cod)(MeCN)] afforded [Rh{κ3 P,Ge,P-GeCl(pyrmPi Pr2 )2 CMe2 }(MeCN)] (3). The methoxidogermyl and methylgermyl rhodium(I) complexes [Rh{κ3 P,Ge,P-GeR(pyrmPi Pr2 )2 CMe2 }(PPh3 )] (R=OMe, 4; Me, 5) were prepared by treating complex 2 with LiOMe and LiMe, respectively. Complex 5 readily reacted with CO to give the carbonyl rhodium(I) derivative [Rh{κ3 P,Ge,P-GeR(pyrmPi Pr2 )2 CMe2 }(CO)] (6), with HCl, HSnPh3 and Ph2 S2 rendering the pentacoordinate methylgermyl rhodium(III) complexes [RhHX{κ3 P,Ge,P-GeMe(pyrmPi Pr2 )2 CMe2 }] (X=Cl, 7; SnPh3 , 8) and [Rh(SPh)2 {κ3 P,Ge,P-GeMe(pyrmPi Pr2 )2 CMe2 }] (9), respectively, and with H2 to give the hexacoordinate derivative [RhH2 {κ3 P,Ge,P-GeMe(pyrmPi Pr2 )2 CMe2 }(PPh3 )] (10). Complexes 3 and 5 are catalyst precursors for the hydroboration of styrene, 4-vinyltoluene and 4-vinylfluorobenzene with catecholborane under mild conditions.

Reactions of Late First-Row Transition Metal (Fe-Zn) Dichlorides with a PGeP Pincer Germylene.

The reactivity of the PGeP germylene 2,2'-bis(di-isopropylphosphanylmethyl)-5,5'-dimethyldipyrromethane-1,1'-diylgermanium(II), Ge(pyrmPiPr2 )2 CMe2 , with late first-row transition metal (Fe-Zn) dichlorides has been investigated. All reactions led to PGeP pincer chloridogermyl complexes. The reactions with FeCl2 and CoCl2 afforded paramagnetic square planar complexes of formula [MCl{κ3 P,Ge,P-GeCl(pyrmPiPr2 )2 CMe2 }] (M=Fe, Co). While the iron complex maintained an intermediate spin state (S1 ; µeff =3.0 µB ) over the temperature range 50-380 K, the effective magnetic moment of the cobalt complex varied linearly with temperature from 1.9 µB at 10 K to 3.6 µB at 380 K, indicating a spin crossover behavior that involves S1/2 (predominant at T<180 K) and S3/2 (predominant at T>200 K) species. Both cobalt(II) species were detected by electron paramagnetic resonance at T<20 K. The reaction of Ge(pyrmPiPr2 )2 CMe2 with [NiCl2 (dme)] (dme=dimethoxyethane) gave a square planar nickel(II) complex, [NiCl{κ3 P,Ge,P-GeCl(pyrmPiPr2 )2 CMe2 }], whereas the reaction with CuCl2 involved a redox process that rendered a mixture of the germanium(IV) compound GeCl2 (pyrmPiPr2 )2 CMe2 and a binuclear copper(I) complex, [Cu2 {µ-κ3 P,Ge,P-GeCl(pyrmPiPr2 )2 CMe2 }2 ], whose metal atoms are in tetrahedral environments. The reaction of the germylene with ZnCl2 led to the tetrahedral derivative [ZnCl{κ3 P,Ge,P-GeCl(pyrmPiPr2 )2 CMe2 }].

Two Types of σ-Allenyl Complexes from Reactions of Silylenes and Germylenes with Chromium Fischer Alkynyl(alkoxy)carbenes.

The reactivity of amidinatotetrylenes of the type E(tBu2 bzm)R1 (E=Si, Ge; tBu2 bzm=N,N'-bis(tertbutyl)benzamidinate; R1 =alkyl or aryl) with the chromium Fischer alkynylcarbene complexes [Cr{C(OEt)C2 R2 }(CO)5 ] (R2 =Ph; ferrocenyl, Fc) has been studied. At room temperature, two different reaction pathways have been identified: (a) attack of the amidinatotetrylene to the alkynyl C2 atom (γ-attack), which leads to σ-allenyl complexes in which the original Ccarbene atom maintains its attachment to the Cr(CO)5 and OEt groups (compounds 3 E - R 1 - R 2 ), and (b) attack of the amidinatotetrylene to the Ccarbene atom (α-attack), which ends in σ-allenyl complexes in which the original Ccarbene atom is not attached to the metal atom and has been inserted into an E-N bond of the amidinatotetrylene forming an E-C-N-C-N five-membered ring (compounds 4 E - R 1 - R 2 ). It has been found that compounds 3 E - R 1 - R 2 are thermodynamically less stable than their corresponding 4 E - R 1 - R 2 isomers and that some of the former (E=Ge; R1 =CH2 SiMe3 ) can be transformed into the latter upon heating. At high temperatures (>70 °C) the reactions involving bulky amidinatotetrylenes (R1 =Mes, tBu) end in the carbene-substitution products [Cr{E(tBu2 bzm)R1 }(CO)5 ].

Reversible Carbene Insertion into a Ge-N Bond and Insights into CO and Carbene Substitution Reactions Involving Amidinatogermylenes and Fischer Carbene Complexes.

The formation of the five-membered-ring germylene complexes [M(CO)5 {Ge(tBu2 bzamC(OEt)Me)tBu}] (3M ; M=Cr, W), which occurs readily at room temperature from the germylene Ge(tBu2 bzam)tBu (1tBu ) and Fischer carbenes [M(CO)5 {C(OEt)Me}] (2M ; M=Cr, W), has been found to be reversible. Upon heating at 60 °C, complexes 3M undergo epimerization to an equilibrium mixture of 3M and 3'M . At that temperature, the chromium epimers (but not the tungsten ones) release CO to end in the mixed germylene-Fischer carbene complexes [Cr(CO)4 {C(OEt)Me}{Ge(tBu2 bzam)tBu}] (cis-4Cr and trans-4Cr ). The latter decompose at 120 °C to [Cr(CO)5 {Ge(tBu2 bzam)tBu}] (6Cr ). Because the formation of cis-4Cr and trans-4Cr from 3Cr or 3'Cr requires the presence of free 1tBu and 2Cr in the reaction solutions, the reactions of 1tBu with 2M to give 3M (and 3'M at 60 °C) should be reversible. This proposal has been proven by germylene-exchange crossover reactions in which free 1tBu and [M(CO)5 {Ge(tBu2 bzamC(OEt)Me)CH2 SiMe3 }] (5'M ; M=Cr, W) were formed when complexes 3M were treated at room temperature with the germylene Ge(tBu2 bzam)CH2 SiMe3 (1tmsm ). A clear differential behavior between N-heterocyclic carbenes (NHCs) and amidinatogermylenes (1tBu and 1tmsm ) in their reactivity against group 6 metal Fischer carbene complexes is demonstrated. The higher electron-donor capacity of amidinatogermylenes with respect to NHCs and the bias of the former to get involved in ring expansion processes are responsible for this differential behavior.

Unexpected Zwitterionic Allenyls from Silylenes and a Fischer Alkynylcarbene: A Remarkable Silylene-Promoted Rearrangement.

The silylenes Si(tBu2 bzam)R (tBu2 bzam=N,N'-bis(tertbutyl)benzamidinate; R=mesityl, CH2 SiMe3 ) attack the Ccarbene atom of the Fischer alkynyl(ethoxy)carbene complex [W(CO)5 {C(OEt)C2 Ph}] to give, after a striking rearrangement, zwitterionic σ-allenyl complexes in which the original carbene C atom forms part of the allene C3 fragment and also of a Si-C-N-C-N five-membered ring after insertion into a Si-N bond of the original amidinatosilylene. These remarkable allenyl products, which contain two stereogenic groups, are selectively formed as single diastereomers.

A Germylene Supported by Two 2-Pyrrolylphosphane Groups as Precursor to PGeP Pincer Square-Planar Group†10 Metal(II) and T-Shaped Gold(I) Complexes.

An efficient synthesis of 2-di-tert-butylphosphanylmethylpyrrole (HpyrmPtBu2 ), by treating 2-dimethylaminomethylpyrrole (HpyrmNMe2 ) with tBu2 PH at 135 °C in the absence of any solvent, has allowed the preparation of the new PGeP germylene Ge(pyrmPtBu2 )2 (1), by treating [GeCl2 (dioxane)] with LipyrmPtBu2 , in which the Ge atom is stabilized by intramolecular interactions with one (solid state) or both (solution) of its phosphane groups. Reactions of germylene 1 with Group 10 metal dichlorido complexes containing easily displaceable ligands have led to [MCl{κ3 P,Ge,P-GeCl(pyrmPtBu2 )2 }] [M=Ni (2), Pd (3), Pt (4)], which have an unflawed square-planar metal environment. Treatment of germylene 1 with [AuCl(tht)] (tht=tetrahydrothiophene) rendered [Au{κ3 P,Ge,P-GeCl(pyrmPtBu2 )2 }] (5), which is a rare case of a T-shaped gold(I) complex. The hydrolysis of 5 gave the linear gold(I) derivative [Au(κP-HpyrmPtBu2 )2 ]Cl (6). Complexes 2-5 contain a PGeP pincer chloridogermyl ligand that arises from the insertion of the Ge atom of germylene 1 into a M-Cl bond of the corresponding metal reagent. The bonding in these molecules has been studied by DFT/NBO/QTAIM calculations. These results demonstrate that the great flexibility of germylene 1 makes it a better precursor to PGeP pincer complexes than the previously known germylenes of this type.

From a Diphosphanegermylene to Nickel, Palladium, and Platinum Complexes Containing Germyl PGeP Pincer Ligands.

The PGeP pincer-type germylene Ge(NCH2 PtBu2 )C6 H4 (1) has been used to prepare a family of group 10 metal complexes, namely, [MCl{κ3 P,Ge,P-GeCl(NCH2 PtBu2 )2 C6 H4 }] (M=Ni (2Ni ), Pd (2Pd ), Pt (2Pt )), featuring a chloridogermyl PGeP pincer ligand and a Cl-Ge-M-Cl bond sequence. Their reactivity is not initially centered on the metal atom but on their Ge atom. Complexes 2Ni and 2Pd easily led to the hydrolyzed products [Ni2 Cl2 {µ-(κ3 P,Ge,P-Ge(NCH2 PtBu2 )2 C6 H4 )2 O}], which features a Cl-Ni-Ge-O-Ge-Ni-Cl bond sequence, and [PdCl{κ3 P,Ge,P-Ge(OH)(NCH2 PtBu2 )2 C6 H4 }], which contains a hydroxidogermyl PGeP pincer ligand (2Pt is reluctant to undergo hydrolysis). Simple chloride exchange reactions led to the methoxidogermyl, methylgermyl, and phenylgermyl derivatives [MCl{κ3 P,Ge,P-GeR(NCH2 PtBu2 )2 C6 H4 }] (M=Pd, Pt; R=OMe, Me, Ph). Whereas the palladium complexes [PdCl{κ3 P,Ge,P-GeR(NCH2 PtBu2 )2 C6 H4 }] (R=Me, Ph) reacted with more MeLi or PhLi to give palladium black and GeR2 (NCH2 PtBu2 )2 C6 H4 (R=Me, Ph), similar reactions with the analogous platinum complexes afforded the transmetalation derivatives [PtR{κ3 P,Ge,P-GeR(NCH2 PtBu2 )2 C6 H4 }] (R=Me, Ph). The short length of the CH2 PtBu2 arms of the PGeP pincer ligands forces the metal atoms of all these complexes to be in a very distorted square-planar ligand environment. The reactivity results have been rationalized with theoretical calculations.

First Insertions of Carbene Ligands into Ge-N and Si-N Bonds.

The insertion of carbene ligands into Ge-N (three examples) and Si-N (one example) bonds has been achieved for the first time by treating Fischer carbene complexes (M=W, Cr) with bulky amidinatotetrylenes (E=Ge, Si). These reactions, which start with a nucleophilic attack of the amidinatotetrylene heavier group 14 atom to the carbene C atom, proceed through a stereoselective insertion of the carbene fragment into an E-N bond of the amidinatotetrylene ENCN four-membered ring, leading to [M(CO)5 L] derivatives in which L belongs to a novel family of tetrylene ligands comprising an ECNCN five-membered ring.

2-(Methylamido)pyridine-Borane: A Tripod κ(3)-N,H,H Ligand in Trigonal Bipyramidal Rhodium(I) and Iridium(I) Complexes with an Asymmetric Coordination of Its BH3 Group.

The complexes [M(κ(3)-N,H,H-mapyBH3)(cod)] (M = Rh, Ir; HmapyBH3 = 2-(methylamino)pyridine-borane; cod = 1,5-cyclooctadiene), which contain a novel anionic tripod ligand coordinated to the metal atom through the amido N atom and through two H atoms of the BH3 group, were prepared by treating the corresponding [M2(µ-Cl)2(cod)2] (M = Rh, Ir) precursor with K[mapyBH3]. X-ray diffraction studies and a theoretical Quantum Theory of Atoms in Molecules analysis of their electron density confirmed that the metal atoms of both complexes are in a very distorted trigonal bipyramidal coordination environment, in which two equatorial sites are asymmetrically spanned by the H-B-H fragment. While both 3c-2e BH-M interactions are more κ(1)-H (terminal σ coordination of the B-H bond) than κ(2)-H,B (agostic-type coordination of the B-H bond), one BH-M interaction is more agostic than the other, and this difference is more marked in the iridium complex than in the rhodium one. This asymmetry is not evident in solution, where the cod ligand and the BH3 group of these molecules participate in two concurrent dynamic processes of low activation energies (variable-temperature NMR and density functional theory studies), namely, a rotation of the cod ligand that interchanges its two alkene fragments (through a square pyramidal transition state) and a rotation of the BH3 group about the B-N bond that equilibrates the three B-H bonds (through a square planar transition state). While the cod rotation has similar activation energy in 2 and 3, the barrier to the BH3 group rotation is higher in the iridium complex than in the rhodium one.

Fully Borylated Methane and Ethane by Ruthenium-Mediated Cleavage and Coupling of CO.

Many transition-metal complexes and some metal-free compounds are able to bind carbon monoxide, a molecule which has the strongest chemical bond in nature. However, very few of them have been shown to induce the cleavage of its C-O bond and even fewer are those that are able to transform CO into organic reagents with potential in organic synthesis. This work shows that bis(pinacolato)diboron, B2pin2, reacts with ruthenium carbonyl to give metallic complexes containing borylmethylidyne (CBpin) and diborylethyne (pinBC≡CBpin) ligands and also metal-free perborylated C1 and C2 products, such as C(Bpin)4 and C2 (Bpin)6, respectively, which have great potential as building blocks for Suzuki-Miyaura cross-coupling and other reactions. The use of (13)CO-enriched ruthenium carbonyl has demonstrated that the boron-bound carbon atoms of all of these reaction products arise from CO ligands.

Reactivity Studies on a Binuclear Ruthenium(0) Complex Equipped with a Bridging κ(2)N,Ge-Amidinatogermylene Ligand.

The amidinatogermylene-bridged diruthenium(0) complex [Ru2{µ-κ(2)Ge,N-Ge((i)Pr2bzam)(HMDS)}(CO)7] (2; (i)Pr2bzam = N,N'-bis(iso-propyl)benzamidinate; HMDS = N(SiMe3)2) reacted at room temperature with (t)BuNC and PMe3 to give [Ru2{µ-κ(2)Ge,N-Ge((i)Pr2bzam)(HMDS)}(L)(CO)6] (L = (t)BuNC, 3; PMe3, 4), which contain the new ligand in an axial position on the Ru atom that is not attached to the amidinato fragment. At 70 °C, 2 reacted with PPh3, PMe3, dppm, and dppe to give the equatorially substituted derivatives [Ru2{µ-κ(2)Ge,N-Ge((i)Pr2bzam)(HMDS)}(L)(CO)6] (L = PPh3, 5; PMe3, 6) and [Ru2{µ-κ(2)Ge,N-Ge((i)Pr2bzam)(HMDS)}(µ-κ(2)P,P'-L2)(CO)5] (L2 = dppm, 7; dppe, 8). HSiEt3 and HSnPh3 were oxidatively added to complex 2 at 70 °C, leading to the coordinatively unsaturated products [Ru2(ER3)(µ-H){µ-κ(2)Ge,N-Ge((i)Pr2bzam)(HMDS)}(CO)5] (ER3 = SiEt3, 9; SnPh3, 10), which easily reacted with (t)BuNC and CO to give the saturated derivatives [Ru2(ER3)(µ-H){µ-κ(2)Ge,N-Ge((i)Pr2bzam)(HMDS)}((t)BuNC)(CO)5] (ER3 = SiEt3, 11; SnPh3, 12) and [Ru2(ER3)(µ-H){µ-κ(2)Ge,N-Ge((i)Pr2bzam)(HMDS)}(CO)6] (ER3 = SiEt3, 13; SnPh3, 14), respectively. Compounds 9-14 have their ER3 group on the Ru atom that is not attached to the amidinato fragment. In contrast, the reaction of 2 with H2 at 70 °C led to the unsaturated tetranuclear complex [Ru4(µ-H)2{µ-κ(2)Ge,N-Ge((i)Pr2bzam)(HMDS)}2(CO)10] (15), which also reacted with (t)BuNC and CO to give the saturated derivatives [Ru4(µ-H)2{µ-κ(2)Ge,N-Ge((i)Pr2bzam)(HMDS)}2(L)2(CO)10] (L = (t)BuNC, 16; CO, 17). All tetraruthenium complexes contain an unbridged metal-metal connecting two germylene-bridged diruthenium units. Under CO atmosphere, complex 17 reverted to compound 2. All of the coordinatively unsaturated products (9, 10, and 15) have their unsaturation(s) located on the Ru atom(s) that is(are) attached to the amidinato fragment(s). In the absence of added reagents, the thermolysis of 2 in refluxing toluene led to [Ru4{µ-κ(2)Ge,N-Ge((i)Pr2bzam)(HMDS)}{µ3-κGe-Ge(HMDS)}(µ-κ(3)N,C,N'-(i)Pr2bzam)(µ-CO)(CO)8] (18), which contains two new ligands, a triply bridging germylidyne and a bridging benzamidinate, and that results from the condensation of two molecules of 2 and the activation of the Ge-N bond of the benzamidinatogermylene ligand of 2.

Amidinatogermylene derivatives of ruthenium carbonyl: new insights into the reactivity of [Ru3(CO)12] with two-electron-donor reagents of high basicity.

The reactivity of ruthenium carbonyl with amidinatogermylenes of the type Ge(R2bzam)(t)Bu (R2bzam = N,N'-disubstituted benzamidinate) was studied for R = (t)Bu (1tBu) and (i)Pr (1iPr). The mono-, bi-, and/or trinuclear derivatives [Ru(1R)(CO)4], [Ru(1R)2(CO)3], [Ru2(1iPr)(CO)7], [Ru3(1tBu)(CO)11], [Ru3(1tBu)2(CO)10], and [Ru3(1R)3(CO)9] (R = (t)Bu, (i)Pr) were isolated in yields that depend upon the reactant ratio and the reaction temperature. The experimental data are consistent with the proposal that, at room temperature, the trinuclear complexes [Ru3(CO)12], [Ru3(1R)(CO)11], and [Ru3(1R)2(CO)10] form an adduct with the germylene 1R that may evolve through two different reaction pathways, (a) releasing a CO ligand (thus leading to the corresponding trinuclear CO-substituted product) and/or (b) cleaving the cluster framework (thus leading to mononuclear germylene-containing products). At 90 °C, additional processes are also possible, such as the reactions of 1R with [Ru(1R)(CO)4] or [Ru3(1R)3(CO)9], which both give [Ru(1R)2(CO)3], or the reactions of [Ru(1tBu)(CO)4] and [Ru(1iPr)(CO)4] with [Ru3(CO)12], which give [Ru3(1tBu)(CO)11] and [Ru2(1iPr)(CO)7], respectively. This wide reaction panorama helps rationalize previously reported outcomes of reactions of [Ru3(CO)12] with other reagents of high basicity, such as trialkylphosphines or N-heterocyclic carbenes, including results for which no satisfactory explanation has been hitherto provided.

Ring opening and bidentate coordination of amidinate germylenes and silylenes on carbonyl dicobalt complexes: the importance of a slight difference in ligand volume.

The reactions of [Co2 (CO)8 ] with one equiv of the benzamidinate (R2 bzam) group-14 tetrylenes [M(R2 bzam)(HMDS)] (HMDS=N(SiMe3 )2 ; 1: M=Ge, R=iPr; 2: M=Si, R=tBu; 3: M=Ge, R=tBu) at 20 °C led to the monosubstituted complexes [Co2 {κ(1) MM(R2 bzam)(HMDS)}(CO)7 ] (4: M=Ge, R=iPr; 5: M=Si, R=tBu; 6: M=Ge, R=tBu), which contain a terminal κ(1) M-tetrylene ligand. Whereas the Co2 Si and Co2 Ge tert-butyl derivatives 5 and 6 are stable at 20 °C, the Co2 Ge isopropyl derivative 4 evolved to the ligand-bridged derivative [Co2 {µ-κ(2) Ge,N-Ge(iPr2 bzam)(HMDS)}(µ-CO)(CO)5 ] (7), in which the Ge atom spans the CoCo bond and one arm of the amidinate fragment is attached to a Co atom. The mechanism of this reaction has been modeled with the help of DFT calculations, which have also demonstrated that the transformation of amidinate-tetrylene ligands on the dicobalt framework is negligibly influenced by the nature of the group-14 metal atom (Si or Ge) but is strongly dependent upon the volume of the amidinate NR groups. The disubstituted derivatives [Co2 {κ(1) MM(R2 bzam)(HMDS)}2 (CO)6 ] (8: M=Ge, R=iPr; 9: M=Si, R=tBu; 10: M=Ge, R=tBu), which contain two terminal κ(1) M-tetrylene ligands, have been prepared by treating [Co2 (CO)8 ] with two equiv of 1-3 at 20 °C. The IR spectra of 8-10 have shown that the basicity of germylenes 1 and 3 is very high (comparable to that of trialkylphosphanes and 1,3-diarylimidazol-2-ylidenes), whereas that of silylene 2 is even higher.

Conversion of a monodentate amidinate-germylene ligand into chelating imine-germanate ligands (on mononuclear manganese complexes).

The unprecedented transformation of a terminal two-electron-donor amidinate-germylene ligand into a chelating three-electron-donor κ(2)-N,Ge-imine-germanate ligand has been achieved by treating the manganese amidinate-germylene complex [MnBr{Ge((i)Pr2bzam)(t)Bu}(CO)4] (1; (i)Pr2bzam = N,N'-bis(isopropyl)benzamidinate) with LiMe or Ag[BF4]. In these reactions, which afford [Mn{κ(2)Ge,N-GeMe((i)Pr2bzam)(t)Bu}(CO)4] (2) and [Mn{κ(2)Ge,N-GeF((i)Pr2bzam)(t)Bu}(CO)4] (3), respectively, the anionic nucleophile, Me(-) or F(-), ends on the Ge atom while an arm of the amidinate fragment migrates from the Ge atom to the Mn atom. In contrast, the reaction of 1 with AgOTf (OTf = triflate) leads to [Mn(OTf){Ge((i)Pr2bzam)(t)Bu}(CO)4] (4), which maintains intact the amidinate-germylene ligand. Complex 4 is very moisture-sensitive, leading to [Mn2{µ-κ(4)Ge2,O2-Ge2(t)Bu2(OH)2O}(CO)8] (5) and [(i)Pr2bzamH2]OTf (6) in wet solvents. In 5, a novel digermanate(II) ligand, [(t)Bu(OH)GeOGe(OH)(t)Bu](2-), doubly bridges two Mn(CO)4 units. The structures of 1-6 have been characterized by spectroscopic (IR, NMR) and single-crystal X-ray diffraction methods.