Introduction of plumbole to f-element chemistry.

Herein, we present the synthesis and characterization of heteroleptic lanthanide complexes bearing a dianionic η5-plumbole ligand in their coordination sphere. The reaction proceeds via a salt elimination reaction between the dilithioplumbole ([Li(thf)]2[1,4-bis-tert-butyl-dimethylsilyl-2,3-bis-phenyl-plumbolyl] = [Li2(thf)2(η5-LPb)]) and specifically designed [Ln(η8-COTTIPS)BH4] precursors (Ln = lanthanide, La, Ce, Sm, Er; COTTIPS = 1,4-bis-triisopropylsilyl-cyclooctatetraenyl), that are capable of stabilizing a planar plumbole moiety in the coordination sphere of different trivalent lanthanide ions. In-depth ab initio calculations show that the aromaticity of the dianionic plumbole is retained upon coordination. Electron delocalization occurs from the plumbole HOMO to an orbital of mainly d-character at the lanthanide ion. The magnetic properties of the erbium congener were investigated in detail, leading to the observation of magnetic hysteresis up to 5 K (200 Oe s-1), an unequivocal proof for single molecule magnet behavior in this system. The magnetic behavior of the erbium species can be modulated by manipulating the position of the lithium cation in the complex, which directly influences the bonding metrics in the central [(η5-LPb)Er(η8-COTTIPS)]- fragment. This allowed us to assess a fundamental magneto-structural correlation in an otherwise identical inner coordination sphere.

Alkali Metal Complexes of a Bis(diphenylphosphino)methane Functionalized Amidinate Ligand: Synthesis and Luminescence.

A novel bis(diphenylphosphino)methane (DPPM) functionalized amidine ligand (DPPM-C(N-Dipp)2 H) (Dipp=2,6-diisopropylphenyl) was synthesized. Subsequent deprotonation with suitable alkali metal bases resulted in the corresponding complexes [M{DPPM-C(N-Dipp)2 }(Ln )] (M=Li, Na, K, Rb, Cs; L=thf, Et2 O). The alkali metal complexes form monomeric species in the solid state, exhibiting intramolecular metal-π-interactions. In addition, a caesium derivative [Cs{PPh2 CH2 -C(N-Dipp)2 }]6 was obtained by cleavage of a diphenylphosphino moiety, forming an unusual six-membered ring structure in the solid state. All complexes were fully characterized by single crystal X-ray diffraction, NMR spectroscopy, IR spectroscopy as well as elemental analysis. Furthermore, the photoluminescent properties of the complexes were thoroughly investigated, revealing differences in emission with regards to the respective alkali metal. Interestingly, the hexanuclear [Cs{PPh2 CH2 -C(N-Dipp)2 }]6 metallocycle exhibits a blue emission in the solid state, which is significantly red-shifted at low temperatures. The bifunctional design of the ligand, featuring orthogonal donor atoms (N vs. P) and a high steric demand, is highly promising for the construction of advanced metal and main group complexes.

d/f-Polypnictides Derived by Non-Classical Ln2+ Compounds: Synthesis, Small Molecule Activation and Optical Properties.

Reduction chemistry induced by divalent lanthanides has been primarily focused on samarium so far. In light of the rich physical properties of the lanthanides, this limitation to one element is a drawback. Since molecular divalent compounds of almost all lanthanides have been available for some time, we used one known and two new non-classical reducing agents of the early lanthanides to establish a sophisticated reduction chemistry. As a result, six new d/f-polyphosphides or d/f-polyarsenides, [K(18-crown-6)] [Cp''2 Ln(E5 )FeCp*] (Ln=La, Ce, Nd; E=P, As) were obtained. Their reactivity was studied by activation of P4 , resulting in a selective expansion of the P5 rings. The obtained compounds [K(18-crown-6)] [Cp''2 Ln(P7 )FeCp*] (Ln=La, Nd) are the first examples of an activation of P4 by a f-element-polypnictide complex. Additionally, the first systematic femtosecond (fs)-spectroscopy investigations of d/f-polypnictides are presented to showcase the advantages of having access to a broader series of lanthanide compounds.

Synthesis of Unprecedented 4d/4f-Polypnictogens.

A series of 4d/4f-polyarsenides, -polyarsines and -polystibines was obtained by reduction of the Mo-pnictide precursor complexes [{Cpt Mo(CO)2 }2 (µ,η2:2 -E2 )] (E=As, Sb; Cpt =tBu substituted cyclopentadienyl) with two different divalent samarocenes [Cp*2 Sm] and [(CpMe4nPr )2 Sm]. For the reductive conversion of the Mo-stibide only one product was isolated, featuring a planar tetrastibacyclobutadiene moiety as an unprecedented ligand for organometallic compounds. For the corresponding Mo-arsenide a tetraarsacyclobutadiene and a second species with a side-on coordinated As2 2- anion was isolated. The latter can be considered as reaction intermediate for the formation of the tetraarsacyclobutadiene.

A bis(germylene) functionalized metal-coordinated polyphosphide and its isomerization.

Pentaphosphaferrocene, [Cp*Fe(η5-P5)] (Cp* = η5-C5Me5), was used as a polyphosphorus source to obtain germylene-polyphosphide complexes. A stepwise reactivity was observed between the di-germylene, [LGe-GeL] (L = {PhC(NtBu)2}), and [Cp*Fe(η5-P5)]. Firstly, reductive homolytic cleavage of the Ge-Ge single bond in [LGe-GeL] led to [(LGe)2{(µ,η4-P5)FeCp*}]. This complex showed an unprecedented isomerization.

3d-4f heterometallic complexes by the reduction of transition metal carbonyls with bulky LnII amidinates.

The redox chemistry between divalent lanthanide complexes bearing bulky amidinate ligands has been studied with 3d transition metal carbonyl complexes (iron and cobalt). The reaction of [(DippForm)2SmII(thf)2] (DippForm = N,N'-bis(2,6-diisopropylphenyl)formamidinate) with [Co2(CO)8] resulted in the formation of a tetranuclear Sm-Co complex, [{(DippForm)2SmIII(thf)}2{(µ-CO)2Co(CO)2}2]. The product of the reaction of [(DippForm)2YbII(thf)2] and [Co2(CO)8] gives the dinuclear Yb-Co complex [{(DippForm)2YbIII(thf)}{(µ-CO)Co(CO)3}] in toluene. The reaction of [(DippForm)2SmII(thf)2] was also carried with the neighbouring group 8 carbonyl complexes [Fe2(CO)9] and [Fe3(CO)12], resulting in a pentanuclear SmIII-Fe complex, [{(DippForm)2SmIII}2{(µ3-CO)2Fe3(CO)9}], featuring a triangular iron carbonyl cluster core.

A Phosphine Functionalized ß-Diketimine Ligand for the Synthesis of Manifold Metal Complexes.

A bis(diphenyl)-phosphine functionalized ß-diketimine (PNac-H) was synthesized as a flexible ligand for transition metal complexes. The newly designed ligand features symmetrically placed phosphine moieties around a ß-diketimine unit, forming a PNNP-type pocket. Due to the hard and soft donor atoms (N vs. P) the ligand can stabilize various coordination polyhedra. A complete series ranging from coordination numbers 2 to 6 was realized. Linear, trigonal planar, square planar, tetrahedral, square pyramidal, and octahedral coordination arrangements containing the PNac-ligand around the metal center were observed by using suitable metal sources. Hereby, PNac-H or its anion PNac- acts as mono-, bi- and tetradendate ligand. Such a broad flexibility is unusual for a rigid tetradentate system. The structural motifs were realized by treatment of PNac-H with a series of late transition metal precursors, for example, silver, gold, nickel, copper, platinum, and rhodium. The new complexes have been fully characterized by single crystal X-ray diffraction, NMR, IR, UV/Vis spectroscopy, mass spectrometry as well as elemental analysis. Additionally, selected complexes were investigated regarding their photophysical properties. Thus, PNac-H proved to be an ideal ligand platform for the selective coordination and stabilization of various metal ions in diverse polyhedra and oxidation states.

Regioselective Insertion of Aluminum(I) in the cyclo-P5 Ring of Pentaphosphaferrocene.

A route to directly access mixed Al-Fe polyphosphide complexes was developed. The reactivity of pentaphosphaferrocene, [Cp*Fe(η5 -P5 )] (Cp*=C5 Me5 ), with two different low-valent aluminum compounds was investigated. The steric and electronic environment around the [AlI ] centre are found to be crucial for the formation of the resulting Al-Fe polyphosphides. Reaction with the sterically demanding [Dipp-BDIAlI ] (Dipp-BDI={[2,6-i Pr2 C6 H3 NCMe]2 CH}- ) resulted in the first Al-based neutral triple-decker type polyphosphide complex. For [(Cp*AlI )4 ], an unprecedented regioselective insertion of three [Cp*AlIII ]2+ moieties into two adjacent P-P bonds of the cyclo-P5 ring of [Cp*Fe(η5 -P5 )] was observed. The regioselectivity of the insertion reaction could be rationalized by isolating an analogue of the reaction intermediate stabilized by a strong σ-donor carbene.

A dimolybdenum paddlewheel as a building block for heteromultimetallic structures.

Diphenylphosphine functionalized propionic acid was applied for the synthesis of heteromultimetallic dimolybdenum(ii) complexes. The ligand features both carboxylic acid and phosphine functionalities, allowing the selective synthesis of a tetracarboxylate bridged Mo2(ii)-paddlewheel structure in a first step. Due to the symmetrically arranged phosphine functionalities, the dimolybdenum(ii) complex was utilized as a metalloligand. Subsequent coordination of late transition metal ions, such as gold(i), rhodium(i), iridium(i) or ruthenium(ii) to the phosphine moieties allowed the formation of heteromultimetallic structures. The flexibility of the diphenylphosphino propionate ligand system enabled intermolecular aurophilic interactions in the Au(i) functionalized dimolybdenum(ii) complexes. Depending on the Au(i) species applied, either a dimeric structure or a 1D coordination polymer was formed in the solid state. These structures represent the first examples of heterometallic dimolybdenum(ii) complexes, forming supramolecular structures via aurophilic interactions.

Neutral and cationic enantiopure group 13 iminophosphonamide complexes.

Synthesis and reactivity of enantiopure iminophosphonamide ligand L-H (L = [Ph2P{N(R)CH(CH3)Ph}2]) with group 13 metal compounds has been investigated. The reaction of L-H with LiAlH4 afforded the aluminium monohydride complex [L2AlH]. The monochloride complexes [L2MCl] (M = Al, Ga) were accessed by reacting corresponding MCl3 (M = Al, Ga) with L-Li. Furthermore, the tetracoordinated aluminium cation [L2Al]+[GaCl4]- and gallium cation [L2Ga]+[AlCl4]- were obtained by chloride abstraction from [L2MCl] (M = Al, Ga), respectively. The title complexes represent the first examples of enantiopure group 13 metal complexes coordinated by chiral iminophosphonamides. All complexes have been characterized by single crystal X-ray diffraction, multinuclear NMR, EA and IR studies.

A cyclopentadienyl functionalized silylene - a flexible ligand for Si- and C-coordination.

The synthesis of a 1,2,3,4-tetramethylcyclopentadienyl (Cp4) substituted four-membered N-heterocyclic silylene [{PhC(NtBu)2}Si(C5Me4H)] is reported first. Then, selected reactions with transition metal and a calcium precursor are shown. The proton of the Cp4-unit is labile. This results in two different reaction pathways: (1) deprotonation and (2) rearrangement reactions. Deprotonation was achieved by the reaction of [{PhC(NtBu)2}Si(C5Me4H)] with suitable zinc precursors. Rearrangement to [{PhC(NtBu)2}(C5Me4)SiH], featuring a formally tetravalent silicon R2C[double bond, length as m-dash]Si(R')-H unit, was observed when the proton of the Cp4 ring was shifted from the Cp4-ring to the silylene in the presence of a Lewis acid. This allows for the coordination of the Cp4-ring to a calcium compound. Furthermore, upon reaction with transition metal dimers [MCl(cod)]2 (M = Rh, Ir; cod = 1,5-cyclooctadiene) the proton stays at the Cp4-ring and the silylene reacts as a sigma donor, which breaks the dimeric structure of the precursors.

Highly Selective Substitution and Insertion Reactions of Silylenes in a Metal-Coordinated Polyphosphide.

Selective substitution and insertion reactions of silylenes into the cyclo-P5 ring of [Cp*Fe(η5-P5)] are reported. The selective substitution of one P atom by an isoelectronic [LSi] fragment (L = PhC(NtBu)2) leads to [(η4-P4SiL)FeCp*] and [LSi(Cl)═P-SiL(Cl)2]. To elucidate the reaction mechanism, [{LSi(N(SiMe3)2)}{(η4-P5)FeCp*}], in which the silicon atom binds to the cyclo-P5 ring, was synthesized as a model compound for the reaction intermediate. The insertion of [LSi-SiL] into the cyclo-P5 ring of [Cp*Fe(η5-P5)] resulted in [{η4-P5(SiL)2}FeCp*] featuring a cyclo-P5(SiL)2 ring, which corresponds to the largest silicon-polyphosphorus ring known in a complex.

Samarium Polyarsenides Derived from Nanoscale Arsenic.

Zintl phases of arsenic and molecular compounds containing Zintl-type polyarsenide ions are of fundamental interest in basic and applied sciences. Unfortunately, the most obvious and reactive arsenic source for the preparation of defined molecular polyarsenide compounds, yellow arsenic As4 , is very inconvenient to prepare and neither storable in pure form nor easy to handle. Herein, we present the synthesis and reactivity of elemental As0 nanoparticles (As0 Nano , d=7.2±1.8 nm), which were successfully utilized as a reactive arsenic source in reductive f-element chemistry. Starting from [Cp*2 Sm] (Cp*=η5 -C5 Me5 ), the samarium polyarsenide complexes [(Cp*2 Sm)2 (µ-η2 :η2 -As2 )] and [(Cp*2 Sm)4 As8 ] were obtained from As0 nano , thereby generating the largest molecular polyarsenide of the f-elements and circumventing the use of As4 in preparative chemistry.

Intensely Photoluminescent Diamidophosphines of the Alkaline-Earth Metals, Aluminum, and Zinc.

The positively charged and weakly polarizable s-block metals commonly do not usually have phosphine ligands in molecular complexes. Herein, we report mono- and dinuclear small diamidophosphine complexes of the alkaline-earth metals Mg, Ca, and Sr, which were prepared from simple precursors and a phosphine-functionalized diamine ligand N,N-bis(2-(diphenyl-phosphino)phenyl)ethane-1,2-diamine (PNHNHP). The alkaline-earth metal based complexes [(PNNP)Mg]2 and [(PNNP)M(thf)3 ] (M=Ca, Sr), exhibit unusual coordination spheres and show bright fluorescence, both in the solid state and in solution. For comparison, the even stronger luminescent Al and Zn complexes [(PNNP)Zn]2 and [(PNNP)AlCl] were prepared. Emission lifetimes in the nanosecond range and high photoluminescence quantum yields up to 93 % are observed at room temperature.

Dimolybdenum Paddlewheel as Scaffold for Heteromultimetallic Complexes: Synthesis and Photophysical Properties.

A diphenylphosphine functionalized benzoic acid was applied for the synthesis of a homoleptic dimolybdenum-based metalloligand, exhibiting four symmetrically placed phosphine donor sites. This allowed subsequent treatment with gold(I), rhodium(I), and iridium(I) precursors to obtain early-late heterometallic complexes as well as Lewis acid-base adducts with BH3. The compounds were in-depth investigated by spectroscopic techniques, single-crystal X-ray diffraction, and femtosecond laser spectroscopy. The coordination of different metal fragments to the dimolybdenum metalloligand leads to a fine-tuning of the system's optical properties, which correlates well with fluorescence quantum yield measurements. Nevertheless, triplet dynamics still remain the dominating channel in these systems with an intersystem crossing time constant below 1 ps.

Reactivity of bulky Ln(ii) amidinates towards P4, As4, and As4S4.

The reduction of P4, As4 and As4S4 (realgar) with the sterically encumbered reductants [(DippForm)2Ln(thf)2] (Ln = Sm, Yb; DippForm = {(2,6-iPr2C6H3)NC(H) = N(2,6-iPr2C6H3)}-) is reported. For the first time, purely f-element containing inverse inorganic sandwich complexes [{(DippForm)2Sm}2(µ2-η4:η4-E4)] (E = P, As), featuring a π-aromatic cyclo [E4]2- middle deck, were obtained upon reaction with P4 and As4. The reaction with realgar leads to a cage disruption and the formation of the unusual species [{(DippForm)(DippForm-AsS2)}Ln(thf)]. The reactivity of divalent Ln amidinates towards main group molecules is in comparison to metallocenes faster, more efficient and thus significantly influenced by the ligand environment. Experimental results are supported by DFT calculations.

Samarium Polystibides Derived from Highly Activated Nanoscale Antimony.

Zintl ions in molecular compounds are of fundamental interest for basic research and application. Two reactive antimony sources are presented that allow direct access to molecular polystibide compounds. These are Sb amalgam (Sb/Hg) and ultrasmall Sb0 nanoparticles (d=6.6±0.8 nm), which were used independently as precursors for the synthesis of the largest f-element polystibide, [(Cp*2 Sm)4 Sb8 ]. Whereas the reaction of the nanoparticles with [Cp*2 Sm] directly led to [(Cp*2 Sm)4 Sb8 ], Sm/Sb/Hg intermediates were isolated when using Sb/Hg as the precursor. These Sm/Sb/Hg intermediates [{(Cp*2 Sm)2 Sb}2 (µ-Hg)] and [{(Cp*2 Sm)3 (µ4 ,η1:2:2:2 -Sb4 )}2 Hg] were synthetically trapped and structurally characterized, giving insight in the formation mechanism of polystibide compounds.

Open Chain Polyarsenides of the Lanthanides.

The reaction of [(Cp'''Co)2 (µ,η2:2 -As2 )2 ] with the decamethylsamarocenes [Cp*2 Sm(THF)2 ] or [Cp*2 Sm], or the bis(tetramethyl-n-propyl)samarocene [(C5 Me4 (n-propyl))2 Sm] resulted in the mixed d/f polyarsenides [(Cp'''Co)2 As4 Sm(η5 -C5 Me4 R)2 ] (R=Me, n-propyl). They are the first structural representatives of open chain-like polyarsenides as ligands in the coordination sphere of lanthanides. Their formation can be explained by an intramolecular As-As coupling within the cobalt polyarsenide complex after reduction by the divalent samarium complex. Density functional theory calculations give insight into the structural change of the (As2 )2 unit in [{Cp'''Co(µ,η2:2 -As2 )}2 ] upon reduction.

Sterically induced reductive linkage of iron polypnictides with bulky lanthanide complexes by ring-opening of THF.

Reduction of [Cp*Fe(η5-E5)] (E = P, As) with divalent lanthanide reagents usually leads to reduction of [Cp*Fe(η5-E5)] followed by a Ln-E bond formation. In contrast, by using the sterically encumbered reagent [(DippForm)2Sm(thf)2] (DippForm = {(2,6-iPr2C6H3)NC(H)[double bond, length as m-dash]N(2,6-iPr2C6H3)}-), ring-opening of thf and reduction of the polypnictide is observed. This leads to two new 3d/4f polyphosphide or polyarsenide complexes [(DippForm)2Sm(Cp*Fe)E5{(CH2)4O}{(DippForm)2Sm(thf)}], in which [(DippForm)2Sm(thf)2] and [Cp*Fe(η5-E5)] are linked by a ring-opened thf molecule and no Ln-E bond formation is observed.

Samarocene oxide: from an undesired decomposition product to a new reagent.

Samarocene oxide [Cp*2Sm-O-SmCp*2] is mostly considered as an undesired decomposition product of the well-established but highly air-sensitive samarocene, [Cp*2Sm(thf)2]. [Cp*2Sm-O-SmCp*2] is often formed by accidental exposure of [Cp*2Sm(thf)2] to air or wet solvents. We show here that [Cp*2Sm-O-SmCp*2] acts as a mild oxide base and thus is a valuable synthetic equivalent for "O(2-)". The reaction of [Cp*2Sm-O-SmCp*2] with the inorganic and organic anhydrides COS, CS2, SO2, SO3, Re2O7, and (PhC(O))2O at room temperature resulted in each case in an O(2-) insertion. The corresponding products were isolated as their samarium complexes.