The Dialuminene AriPr8AlAlAriPr8 (AriPr8 = C6H-2,6-(C6H2-2,4,6-iPr3)2-3,5-iPr2).

Careful analysis of the crystals formed in the reduction of AriPr8AlI2 (AriPr8 = C6H-2,6-(C6H2-2,4,6-iPr3)2-3,5-iPr2) with sodium on sodium chloride showed them to contain the long sought-after dialuminene AriPr8AlAlAriPr8 (1) that forms alongside the previously characterized alanediyl:AlAriPr8. The single crystal X-ray structure of 1 revealed a nearly planar, trans-bent C(ipso)AlAlC(ipso) core with an Al-Al distance of 2.648(2) Å. The molecular and electronic structure of 1 are consistent with a Al-Al double dative interaction augmented with diradical character and stabilized by dispersion interactions. Density functional theory calculations showed that the reactivity of:AlAriPr8 with dihydrogen involves 1, not:AlAriPr8, as the reactive species. In contrast, the reaction of:AlAriPr8 with ethylene gave two products, the 1,4-dialuminacyclohexane AriPr8Al(C2H4)2AlAriPr8 (2) and the aluminacyclopentane AriPr8Al(C4H8) (3), that can both form from the aluminacyclopropane intermediate AriPr8Al(C2H4). Although the [2+2+2] cycloaddition of 1 with two equivalents of ethylene was also calculated to be exergonic, it is likely to be kinetically blocked by the numerous isopropyl substituents surrounding the Al-Al bond. Attempts to fine-tune the steric bulk of the terphenyl ligand to allow stronger Al-Al bonding were unsuccessful, leading to the isolation of the sodium salt of a cyclotrialuminene, Na2[AlAriPr6]3 (4), instead of AriPr6AlAlAriPr6.

Ni(I) and Ni(II) Bis(trimethylsilyl)amides Obtained in Pursuit of the Elusive Structure of Ni{N(SiMe3)2}2.

Salt metathesis routes to five new -N(SiMe3)2 nickel derivatives were studied to illuminate their mode of formation, structures, and spectroscopy. The reaction between NiI2 and K{N(SiMe3)2} afforded the Ni(II) and Ni(I) complexes [K][Ni{N(SiMe3)2}3] (1) and [K][Ni{N(SiMe3)2}2] (2). Dissolving 1 in tetrahydrofuran (THF) gave the Ni(II) species [K(THF)2][Ni{N(SiMe3)2}3] (3). The Ni(I) salt [K(DME)][Ni2{N(SiMe3)2}3] (4) was obtained by using NiCl2(DME) (DME = 1,2-dimethoxyethane) as the nickel source rather than NiI2. The isolation of the Ni(I) complexes 2 and 4 highlights the tendency for K{N(SiMe3)2} to function as a reducing agent. Introduction of adventitious O2 to solutions of [K][Ni{N(SiMe3)2}2] (2) gave the nickel inverse crown ether (ICE) species [K2][O(Ni{N(SiMe3)2}2)2] (5). Complex 5 is the first ICE complex of nickel and is one of four known ICE complexes for the 3d metals. The experimental results indicate that the reduced Ni(I) bis(trimethylsilyl)amides are relatively easily generated, whereas Ni(III) derivatives that might be expected from a disproportionation of a Ni(II) derivative are apparently not yet isolable by the above routes. Overall, the new species crystallize readily from the reaction mixtures, but under ambient conditions, they begin to decompose as solids within ca. 24 h, which hinders their characterization.

Hydrobismuthation: Insertion of Unsaturated Hydrocarbons into the Heaviest Main Group Element Bond to Hydrogen.

The bismuth hydride (2,6-Mes2H3C6)2BiH (1, Mes = 2,4,6-trimethylphenyl), which has a Bi-H 1H NMR spectroscopic signal at δ = 19.64 ppm, was reacted with phenylacetylene at 60 °C in toluene to yield [(2,6-Mes2C6H3)2BiC(Ph)=CH2] (2) after 15 min. Compound 2 was characterized by 1H, 13C NMR, and UV-vis spectroscopy, single crystal X-ray crystallography, and calculations employing density functional theory. Compound 2 is the first example of a hydrobismuthation addition product and displays Markovnikov regioselectivity. Computational methods indicated that it forms via a radical mechanism with an associated Gibbs energy of activation of 91 kJ mol-1 and a reaction energy of -90 kJ mol-1.

Sn(II)-carbon bond reactivity: radical generation and consumption via reactions of a stannylene with alkynes.

Thermal Sn-C cleavage in the diarylstannylene Sn(AriPr4)2 (AriPr4 = C6H3-2,6-(C6H3-2,6-iPr2)2) was used to generate ˙Sn(AriPr4) and ˙AriPr4 radicals for alkyne arylstannylation. The radical pair and RCCR' (R = H, R' = Ph; R = Ph, R' = Ph; R = H, R' = C4H9; R = H, R' = SiMe3) in refluxing benzene generate the aryl vinyl stannylene complexes, AriPr4Sn{C(C6H5)-C(H)(AriPr4)} (1), AriPr4Sn{C(C6H5)-C(H)(C6H5)} (2) and AriPr4Sn{C(C4H9)-C(H)(AriPr4)} (3) respectively. For HCCSiMe3, the known distannene {Sn(CCSiMe3)AriPr4}2 (4) was also generated from this new method.

Correction to "Synthesis, Structure, and Spectroscopy of the Biscarboranyl Stannylenes (bc)Sn·THF and K2[(bc)Sn]2 (bc = 1,1'(ortho-Biscarborane)) and Dibiscarboranyl Ethene (bc)CH=CH(bc)".

[This corrects the article DOI: 10.1021/acs.organomet.3c00190.].

Synthesis, Structure, and Spectroscopy of the Biscarboranyl Stannylenes (bc)Sn·THF and K2[(bc)Sn]2 (bc = 1,1'(ortho-Biscarborane)) and Dibiscarboranyl Ethene (bc)CH=CH(bc).

Two compounds containing a Sn(II) atom supported by a bidentate biscarborane ligand have been synthesized via salt metathesis. The synthetic procedures for (bc)Sn·THF (bc = 1,1' (ortho-carborane) (1) and K2[(bc)Sn]2 (2) involved the reaction of K2[bc] with SnCl2 in either a THF solution (1) or in a benzene/dichloromethane solvent mixture (2). Using the same solvent conditions as those used for 2 but using a shorter reaction time gave a dibiscarboranyl ethene (3). The products were characterized by 1H, 13C, 11B, 119Sn NMR, UV-vis, and IR spectroscopy, and by X-ray crystallography. The diffraction data for 1 and 2 show that the Sn atom has a trigonal pyramid environment and is constrained by the bc ligand in a planar five-membered C4Sn heterocycle. The 119Sn NMR spectrum of 1 displays a triplet of triplets pattern signal, which is unexpected given the absence of a Sn-H signal in the 1H NMR, IR spectrum, and X-ray crystallographic data. However, a comparison with other organotin compounds featuring a Sn atom bonded to carboranes reveal similar multiplets in their 119Sn NMR spectra, likely arising from long-range nuclear spin-spin coupling between the carboranyl 11B and 119Sn nuclei. Compound 3 displays structural and spectroscopic characteristics typical of conjugated alkenes.

Rearrangement of a Ge(II) aryloxide to yield a new Ge(II) oxo-cluster [Ge6(µ3-O)4(µ2-OC6H2-2,4,6-Cy3)4](NH3)0.5: main group aryloxides of Ge(II), Sn(II), and Pb(II) [M(OC6H2-2,4,6-Cy3)2]2 (Cy = cyclohexyl).

The new Ge(II) cluster [Ge6(µ3-O)4(µ2-OC6H2-2,4,6-Cy3)4](NH3)0.5 (1) and three divalent Group 14 aryloxide derivatives [Ge(OC6H2-2,4,6-Cy3)2]2 (2), [Sn(OC6H2-2,4,6-Cy3)2]2 (3), and [Pb(OC6H2-2,4,6-Cy3)2]2 (4) of the new tricyclohexylphenyloxo ligand, [(-OC6H2-2,4,6-Cy3)2]2 (Cy = cyclohexyl), were synthesized and characterized. Complexes 1-4 were obtained by reaction of the metal bissilylamides M(N(SiMe3)2)2 (M = Ge, Sn, Pb) with 2,4,6-tricyclohexylphenol in hexane at room temperature. If the freshly generated reaction mixture for the synthesis of 2 is stirred in solution for 12 h at room temperature, the cluster [Ge6(µ3-O)4(µ2-OC6H2-2,4,6-Cy3)4](NH3)0.5 (1), which features a rare Ge6O8 core that includes ammonia molecules in non-coordinating positions, is formed. Complexes 3 and 4 were also characterized via119Sn{1H} NMR and 207Pb NMR spectroscopy and feature signals at -280.3 ppm (119Sn{1H}, 25 °C) and 1541.0 ppm (207Pb, 37 °C), respectively. The spectroscopic characterization of 3 and 4 extends known 119Sn parameters for dimeric Sn(II) aryloxides, but data for 207Pb NMR spectra for Pb(II) aryloxides are rare. We present also a rare VT-NMR study of a homoleptic 3-coordinate Pb(II) aryloxide. The crystal structures of 2, 3, and 4 feature interligand H⋯H contacts that are similar in number to those of related transition metal derivatives despite the larger size of the group 14 elements.

Mn(II), Fe(II), and Co(II) Aryloxides: Steric and Dispersion Effects and the Thermal Rearrangement of a Cobalt Aryloxide to a Co(II) Semiquinone Complex.

A series of Mn(II), Fe(II), and Co(II) bisaryloxide dimers ([M(OC6H2-2,4,6-Cy3)2]2 {M = Mn (1), Fe (2), and Co (3)} were synthesized by the addition of 2,4,6-tricyclohexylphenol (HOC6H2-2,4,6-Cy3) to the silyl amido dimers [M(N(SiMe3)2)2]2 (M = Mn, Fe, Co; Cy = cyclohexyl). An unexpected and unique Co(II) phenoxide derivative (4), [Co(OC6H2-2,4,6-Cy3)(O2C6H-3,5,6-Cy3)]2, was obtained via ligand rearrangement of 3 at ca. 180 °C. This yielded 4 in which there are two unchanged, bridging phenoxide ligands as well as a terminal bidentate semiquinone ligand bound to each cobalt. Complexes 1 and 2 did not undergo such a rearrangement under the same conditions; both are thermally stable to temperatures exceeding 250 °C and feature numerous short-contact (<2.5 Å) H···H interactions consistent with the presence of dispersion stabilization. Use of the aryloxide ligand -OC6H3-2,6-Pri2 (Pri = isopropyl), which is sterically similar to -OC6H2-2,4,6-Cy3 but produces fewer close H···H interactions, gave the trimeric species [M(OC6H3-2,6-Pri2)2]3 {M = Fe (5) or Co (6)} which feature a linear array of three metal atoms bridged by aryloxides. The higher association number in 5 and 6 in comparison to that of 1-3 is due to the lower dispersion energy donor properties of the -OC6H3-2,6-Pri2 ligand and the lower stabilization it produces.

London Dispersion Effects on the Stability of Heavy Tetrel Molecules.

London dispersion (LD) interactions, which stem from long-range electron correlations arising from instantaneously induced dipoles can occur between neighboring atoms or molecules, for example, between H atoms within ligand C-H groups. These interactions are currently of interest as a new method of stabilizing long bonds and species with unusual oxidation states. They can also limit reactivity by installing LD enhanced groups into organic frameworks or ligand substituents. Here, we address the most recent advances in the design of LD enhanced ligands, the sterically counterintuitive structures that can be generated and the consequences that these interactions can have on the structures and reactivity of sterically crowded heavy group 14 species.

Disproportionation of Sn(II){CH(SiMe3)2}2 to ˙Sn(III){CH(SiMe3)2}3 and ˙Sn(I){CH(SiMe3)2}: characterization of the Sn(I) product.

Half a century after the photolytic disproportionation of Lappert's dialkyl stannylene SnR2, R = CH(SiMe3)2 (1) gave the persistent trivalent radical [˙SnR3], the characterization of the corresponding Sn(I) product, ˙SnR is now described. It was isolated as the hexastannaprismane Sn6R6 (2), from the reduction of 1 by the Mg(I)-reagent, Mg(BDIDip)2 (BDI = (DipNCMe)2CH, Dip = 2,6-diisopropylphenyl).

London Dispersion Effects in a Distannene/Tristannane Equilibrium: Energies of their Interconversion and the Suppression of the Monomeric Stannylene Intermediate.

Reaction of {LiC6 H2 -2,4,6-Cyp3 ⋅Et2 O}2 (Cyp=cyclopentyl) (1) of the new dispersion energy donor (DED) ligand, 2,4,6-triscyclopentylphenyl with SnCl2 afforded a mixture of the distannene {Sn(C6 H2 -2,4,6-Cyp3 )2 }2 (2), and the cyclotristannane {Sn(C6 H2 -2,4,6-Cyp3 )2 }3 (3). 2 is favored in solution at higher temperature (345 K or above) whereas 3 is preferred near 298 K. Van't Hoff analysis revealed the 3 to 2 conversion has a ΔH=33.36 kcal mol-1 and ΔS=0.102 kcal mol-1 K-1 , which gives a ΔG300 K =+2.86 kcal mol-1 , showing that the conversion of 3 to 2 is an endergonic process. Computational studies show that DED stabilization in 3 is -28.5 kcal mol-1 per {Sn(C6 H2 -2,4,6-Cyp3 )2 unit, which exceeds the DED energy in 2 of -16.3 kcal mol-1 per unit. The data clearly show that dispersion interactions are the main arbiter of the 3 to 2 equilibrium. Both 2 and 3 possess large dispersion stabilization energies which suppress monomer dissociation (supported by EDA results).

Comproportionation of a dialuminyne with alane or dialane dihalides as a clean route to dialuminenes.

Dialuminenes RAlAlR (R = m-terphenyl or bulky aryl) react with the aromatic solvents (e.g. benzene or toluene) in which they dissolve. We synthesized -SiMe3 substituted derivatives of known terphenyl ligands to increase their solubility in alkanes which have lower reactivity than arenes. The new dialuminene was synthesized via the comproportionation reaction of Na2(AlAriPr4-4-SiMe3)2 (3) (AriPr4-4-SiMe3 = 2,6-(2,6-iPr2C6H3)2-4-SiMe3C6H2) with either the diiodide Al(Et2O)I2AriPr4-4-SiMe3 (1) or the 1,2-diiododialane 4-SiMe3AriPr4(I)Al-Al(I)AriPr4-4-SiMe3 (2). This cleanly generates the dialuminene 4-SiMe3AriPr4AlAlAriPr4-4-SiMe3 which was trapped as its cycloaddition product (4) with benzene. Even in non-aromatic, essentially inert, solvents red 4 decomposes to colorless solutions. This indicates that the instability of the free dialuminene is an inherent property rather than arising from of the method of synthesis, solvent employed, or the presence of impurities.

Terpene dispersion energy donor ligands in borane complexes.

Structural characterization of the complex [B(ß-pinane)3] (1) reveals non-covalent H⋯H contacts that are consistent with the generation of London dispersion energies involving the ß-pinane ligand frameworks. The homolytic fragmentations of 1, and camphane and sabinane analogues ([B(camphane)3] (2) and [B(sabinane)3] (3)) were studied computationally. Isodesmic exchange results showed that London dispersion interactions are highly dependent on the terpene's stereochemistry, with the ß-pinane framework providing the greatest dispersion free energy (ΔG = -7.9 kcal mol-1) with Grimme's dispersion correction (D3BJ) employed. PMe3 was used to coordinate to [B(ß-pinane)3], giving the complex [Me3P-B(ß-pinane)3] (4), which displayed a dynamic coordination equilibrium in solution. The association process was found to be slightly endergonic at 302 K (ΔG = +0.29 kcal mol-1).

Beyond Steric Crowding: Dispersion Energy Donor Effects in Large Hydrocarbon Ligands.

Interactions between sterically crowded hydrocarbon-substituted ligands are widely considered to be repulsive because of the intrusion of the electron clouds of the ligand atoms into each other's space, which results in Pauli repulsion. Nonetheless, there is another interaction between the ligands which is less widely publicized but is always present. This is the London dispersion (LD) interaction which can occur between atoms or molecules in which dipoles can be induced instantaneously, for example, between the H atoms from the ligand C-H groups.These LD interactions are always attractive, but their effects are not as widely recognized as those of the Pauli repulsion despite their central role in the formation of condensed matter. Their relatively poor recognition is probably due to the relative weakness (ca. 1 kcal mol-1) of individual H···H interactions owing to their especially strong distance dependence. In contrast, where there are numerous H···H interactions, a collective LD energy equaling several tens of kcal mol-1 may ensue. As a result, in some molecules the latent importance of the LD attraction energies emerges and assumes a prominence that can overshadow the Pauli effects (e.g., in the stabilization of high-oxidation-state transition-metal alkyls, inducing disproportionation reactions, or in the stabilization of otherwise unstable bonds).Despite being known for over a century, the accurate quantification of individual H···H LD effects in molecular species is a relatively recent phenomenon and at present is based mainly on modified DFT calculations. A few leading reviews summarized these earlier studies of the C-H···H-C LD interactions in organic molecules, and their effects on the structures and stabilities were described. LD effects in sterically crowded inorganic and organometallic molecules have been recognized.The author's interest in these LD effects arose fortuitously over a decade ago during research on sterically crowded heavier main-group element carbene analogues and two-coordinate, open-shell (d1-d9) transition-metal complexes where counterintuitive steric effects were observed. More detailed explanations of these effects were provided by dispersion-corrected DFT calculations in collaboration with the groups of Tuononen and Nagase (see below).This Account describes our development of these initial results for other inorganic molecular classes. More recently, the work has led us to move to the planned inclusion of dispersion effects in ligands to stabilize new molecular types with theoretical input from the groups of Vasko and Grimme (see below). Our approach sought to use what Grimme has described as dispersion effect donor (DED) groups (i.e., spatially close-lying, densely packed substituents either as ligands (e.g., -C6H2-2,4,6-Cy3, Cy = cyclohexyl) or as parts of ligands (e.g., a Cy substituent) that produce relatively large dispersion energies to stabilize these new compounds.We predict that the future design of sterically crowding hydrocarbon ligands will include the consideration and incorporation of LD effects as a standard methodology for directed use in the attainment of new synthetic targets.

Inhibition of Alkali Metal Reduction of 1-Adamantanol by London Dispersion Effects.

A series of alkali metal 1-adamantoxide (OAd1 ) complexes of formula [M(OAd1 )(HOAd1 )2 ], where M=Li, Na or K, were synthesised by reduction of 1-adamantanol with excess of the alkali metal. The syntheses indicated that only one out of every three HOAd1 molecules was reduced. An X-ray diffraction study of the sodium derivative shows that the complex features two unreduced HOAd1 donors as well as the reduced alkoxide (OAd1 ), with the Ad1 fragments clustered together on the same side of the NaO3 plane, contrary to steric considerations. This is the first example of an alkali metal reduction of an alcohol that is inhibited from completion due to the formation of the [M(OAd1 )(HOAd1 )2 ] complexes, stabilized by London dispersion effects. NMR spectroscopic studies revealed similar structures for the lithium and potassium derivatives. Computational analyses indicate that decisive London dispersion effects in the molecular structure are a consequence of the many C-H⋅⋅⋅H-C interactions between the OAd1 groups.

Designing a Solution-Stable Distannene: The Decisive Role of London Dispersion Effects in the Structure and Properties of {Sn(C6H2-2,4,6-Cy3)2}2 (Cy = Cyclohexyl).

The reaction of 1 equiv of the dimeric lithium salt of a new London dispersion effect donor ligand {Li(C6H2-2,4,6-Cy3)·OEt2}2 (Cy = cyclohexyl) with SnCl2 afforded the distannene {Sn(C6H2-2,4,6-Cy3)2}2 (1). The distannene remains dimeric in solution, as indicated by its room-temperature 119Sn NMR signal (δ = 361.3 ppm) and its electronic spectrum, which is invariant over the temperature range of -10 to 100 °C. The formation of the distannene, which has a short Sn-Sn distance of 2.7005(7) Å and greatly enhanced stability in solution compared to that of other distannenes, is due to increased interligand London dispersion (LD) attraction arising from multiple close approaches of ligand C-H moieties across the Sn-Sn bond. DFT-D4 calculations revealed a dispersion stabilization of dimer 1 of 38 kcal mol-1 and a dimerization free energy of ΔGdimer = -6 kcal mol-1. In contrast, the reaction of 2 equiv of the similarly shaped but less bulky, less hydrogen-rich Li(C6H2-2,4,6-Ph3)·(OEt2)2 with SnCl2 yielded the monomeric stannylene Sn(C6H2-2,4,6-Ph3)2 (2), which is unstable in solution at ambient temperature.

Hydrides, Halides, and Polymers: Some Unexpected Intermediates on the Routes to First-Row Transition Metal M{N(SiMe3)2}n (n = 2, 3) Complexes.

The reaction of 2 equiv of LiN(SiMe3)2·Et2O with TiCl3(NMe3)2 or VCl3(NMe3)2 afforded the dimeric, halide bridged complexes [Ti(µ-Cl){N(SiMe3)2}2]2 (1) or [V(µ-Cl){N(SiMe3)2}2]2 (2) in moderate yields. The reduction of titanium complex 1 with 3 equiv of 5% (wt) Na/NaCl gave the mixed metal titanium/sodium hydride cluster Ti2(µ-H)2{N(SiMe3)2}3{N(SiMe3)(SiMe2CH)}(Na) (3), which was formed by activation of two C-H bonds at a single methyl group of one of the bis(trimethylsilyl)amide ligands. Attempts to form the analogous vanadium complex by reduction of 2 gave only intractable products. Treatment of Co{N(SiMe3)2}2 with 1 equiv of BrN(SiMe3)2 (which was previously shown to give the unique three-coordinate cobalt(III) trisamide Co{N(SiMe3)2}3) afforded the polymeric [(µ-Br)Co{µ-N(SiMe3)(SiMe2CH2CH2Me2Si)(Me3Si)µ-N}Co(µ-Br)]∞ (4) as a second product, which was shown by a structural analysis to possess a carbon-carbon bond formed between the two ligands. Attempts to isolate manganese and iron complexes analogous to 4 were unsuccessful. The role of bromine in these reactions was further studied by examining the reaction of 0.5 equiv of elemental bromine with [Mn{N(SiMe3)2}2]2 or [Co{N(SiMe3)2}2]2, which for manganese was shown to give the previously reported manganese trisamide Mn{N(SiMe3)2}3 but for cobalt gives the dimeric amide-bridged [Co(Br){µ-N(SiMe3)2}]2 (5).

Dimeric Copper and Lithium Thiolates: Comparison of Copper Thiolates with Their Lithium Congeners.

The direct reactions of the large terphenyl thiols HSAriPr4 (AriPr4= -C6H3-2,6-(C6H3-2,6-iPr2)2) and HSAriPr6 (AriPr6= -C6H3-2,6-(C6H2-2,4,6-iPr3)2) with stoichiometric amounts of mesitylcopper(I) in THF at ca. 80 °C afforded the first well-characterized dimeric copper thiolato species {CuSAriPr4}2 (1) and {CuSAriPr6}2 (2) with elimination of mesitylene. The complexes 1 and 2 were characterized by NMR and electronic spectroscopy as well as by X-ray crystallography. They have dimeric Cu2S2 core structures in which the two copper atoms are bridged by the sulfurs from the thiolato ligands and feature short Cu--Cu distances near 2.4 Å as well as a weak copper-flanking aryl ring interaction from a terphenyl substituent. The structures of the planar Cu2S2 cores bear a resemblance to the CuA site in nitrous oxide reductase in which two cysteines also bridge two copper atoms. The related dimeric Li2S2 structural motif was also observed in the lithium congeners {LiSAriPr4}2 (3) and {LiSAriPr6}2 (4) which were synthesized directly from the thiols and n-BuLi in hexanes. However, despite the very similar effective ionic radii of the Li+ (0.59 Å) and Cu+ (0.60 Å) ions, the Li--Li structures display very much longer (by more than ca. 0.5 Å) separations than the corresponding Cu--Cu distances in 1 and 2, which may be due to weaker dispersion interactions.

Hydrostannylation of carbon dioxide by a hydridostannylene molybdenum complex.

Reaction of the aryltin(II) hydrides {AriPr4Sn(µ-H)}2 or {AriPr6Sn(µ-H)}2 (AriPr4 = -C6H3-2,6-(C6H3-2,6-iPr2)2, AriPr6 = -C6H3-2,6-(C6H2-2,4,6-iPr3)2) with two equivalents of the molybdenum carbonyl [Mo(CO)5(THF)] afforded the divalent tin hydride transition metal complexes, Mo(CO)5{Sn(AriPr6)H}, (1), or Mo(CO)5{Sn(AriPr4)(THF)H} (2), respectively. Complex 1 effects the facile hydrostannylation of carbon dioxide, to yield Mo(CO)5{Sn(AriPr6)(κ2-O,O'-O2CH)}, (3), which features a bidentate formate ligand coordinating the tin atom. Reaction of 3 with the pinacolborane, HBpin (pin = pinacolato) in benzene regenerated 1 in quantitative yield. All complexes were characterized by X-ray crystallography, as well as UV-visible, IR, and multinuclear NMR spectroscopies. The isolation of 1 and 2 is consistent with the existence of monomeric forms of {AriPr4Sn(µ-H)}2 and {AriPr6Sn(µ-H)}2 in solution. Regeneration of 1 from 3via reaction with pinacolborane as the hydrogen source shows the catalytic potential of 1 in the hydrogenation of CO2.

Reductions of M{N(SiMe3)2}3 (M = V, Cr, Fe): Terminal and Bridging Low-Valent First-Row Transition Metal Hydrido Complexes and "Metallo-Transamination".

The reaction of the vanadium(III) tris(silylamide) V{N(SiMe3)2}3 with LiAlH4 in diethyl ether gives the highly unstable mixed-metal polyhydride [V(µ2-H)6[Al{N(SiMe3)2}2]3][Li(OEt2)3] (1), which was structurally characterized. Alternatively, performing the same reaction in the presence of 12-crown-4 affords a rare example of a structurally verified vanadium terminal hydride complex, [VH{N(SiMe3)2}3][Li(12-crown-4)2] (2). The corresponding deuteride 2D was also prepared using LiAlD4. In contrast, no hydride complexes were isolated by reaction of M{N(SiMe3)2}3 (M = Cr, Fe) with LiAlH4 and 12-crown-4. Instead, these reactions afforded the anionic metal(II) complexes [M{N(SiMe3)2}3][Li(12-crown-4)2] (3, M = Cr; 4, M = Fe). The reaction of the iron(III) tris(silylamide) Fe{N(SiMe3)2}3 with lithium aluminum hydride without a crown ether gives the "hydrido inverse crown" complex [Fe(µ2-H){N(SiMe3)2}2(µ2-Li)]2 (5), while treatment of the same trisamide with alane trimethylamine complex gives the iron(II) polyhydride complex Fe(µ2-H)6[Al{N(SiMe3)2}2]2[Al{N(SiMe3)2}(NMe3)] (6). Complexes 2-6 were characterized by X-ray crystallography, as well as by infrared, electronic, and 1H and 13C (complex 6) NMR spectroscopies. Complexes 1 and 6 are apparently formed by an unusual "metallo-transamination" process.