Synthesis of the First Examples of Transition Metal .eta.2-SiH4 Complexes, cis-Mo(.eta.2-SiH4)(CO)(R2PC2H4PR2)2, and Evidence for an Unprecedented Tautomeric Equilibrium between an .eta.2-SiH4 Complex and a Hydridosilyl Species: A Model for Methane Coordination and Activation

Matrix Reactivity of Al and Ga Atoms (M) in the Presence of Silane: Generation and Characterization of the η2‐Coordinated Complex M⋅SiH4, the Insertion Product HMSiH3, and the MISpecies MSiH3in a Solid Argon Matrix

“…[1] Examples include species in which the CH 4 or SiH 4 is coordinated to one metal center as, for example, in the first h 2 -SiH 4 transition-metal complex to be characterized, cis-[Mo(h 2 -SiH 4 )(CO)(R 2 PC 2 H 4 PR 2 ) 2 ] (R= Ph, iBu, Et), [2] and others in which the CH 4 or SiH 4 is trapped between two metal centers, as in [(R 3 P) 2 H 2 Ru(SiH 4 )-RuH 2 (PR 3 ) 2 ] (R= Cy or iPr). [3] Remarkably, cis-[Mo(h 2 -SiH 4 )(CO)(Et 2 PC 2 H 4 PEt 2 ) 2 ] is reported [2] to enter into equilibrium with its tautomer [MoH(SiH 3 )(CO)(Et 2 PC 2 H 4 -PEt 2 ) 2 ], which features a seven-coordinate Mo center, as evidenced by the 1 H and 31 P NMR spectra of the solutions at different temperatures. Quantum chemical studies indicate that bonding in these SiH 4 complexes occurs through 1) a dative bond involving the s(Si À H) orbital and a vacant metal (M) orbital of appropriate symmetry, and 2) d (M)!…”

“…The preferred geometry is characterized by a planar HGa(m-Si)Ga skeleton and conforms overall to C s symmetry; the dimensions computed for this and the slightly less favored isomer V are given in Figure 7. The system Ga 2 SiH 4 thus contrasts with Ga 2 H 2 , for which all the corresponding isomers are represented by stable minima on the potential-energy hypersurface; here the global minimum corresponds to the tetracyclic Ga(m-H) 2 Ga which, together with GaGaH 2 and trans-HGaGaH, has been identified experimentally. [30] The instability of IV must reflect the incompatibility of the bridging requirements of the H and SiH 3 ligands.…”

“…Among these were bands at 1571.6, 1578.4, and 1002 cm À1 recognizable as belonging to the known species Ga¥H 2 O (A. J. Downs, V. A. Macrae, unpublished results, and ref. [29]), and Ga(m-H) 2 Ga, [30] respectively. In circumstances in which Ga 2 ¥H 2 O and Ga(m-H) 2 Ga were relatively conspicuous, it was noticeable that 4 b was present in some abundance.…”

“…[29]), and Ga(m-H) 2 Ga, [30] respectively. In circumstances in which Ga 2 ¥H 2 O and Ga(m-H) 2 Ga were relatively conspicuous, it was noticeable that 4 b was present in some abundance. All the signs suggest therefore that 4 b is the product of a spontaneous reaction of SiH 4 , not with Ga atoms but with Ga 2 dimers.…”

Binding of hydrocarbons and other extremely weak ligands to transition metal complexes that coordinate hydrogen: Investigation of cis-interactions and delocalized bonding involving sigma bonds

“…Importantly, these are the first systems in which H2, silane, and agostic C-H bonding is observed on the same metalfragment.. This allows direct comparison of bond activation and shows that more backbonding is needed to both stabilize and cleave Si-H bonds Thefirst examples of stable metal SiH4 complexes, 4u, were discovered [2]:…”