Conversion of a Diruthenium μ-Methylene Complex, Cp₂Ru₂(μ-CH₂)(μ-CO)(CO)₂, into Methane through Reduction with Hydrosilane:  Reactivity of Silyl−μ-Methylene Intermediates Cp₂Ru₂(μ-CH₂)(SiR₃)(X)(CO)₂(X = H, SiR₃) Relevant to Catalytic CO Hydrogenation and Activation of Si−H, C−H, and C−Si Bonds

Abstract

Thermolysis (170 °C, 3 days) of a diruthenium µ-methylene complex, Cp 2 Ru 2 (µ-CH 2 )(µ-CO)(CO) 2 (1), in the presence of HSiMe 3 produces methane along with methylsilane (SiMe 4 ) and mononuclear organometallic products, CpRu(H)(SiR 3 ) 2 (CO) (2) and CpRu(CO) 2 (SiMe 3 ) (3). The reaction mechanism involving initial CO dissociation has been investigated by using a labile µ-methylene species, Cp 2 Ru 2 (µ-CH 2 )(µ-CO)(CO)(MeCN) (4), the MeCN adduct of the coordinatively unsaturated species resulting from decarbonylation of 1. Treatment of 4 with HSiR 3 produces the hydrido-silyl-µ-methylene intermediate Cp 2 Ru 2 (µ-CH 2 )(H)(SiR 3 )(CO) 2 (5) and the disilyl-µ-methylene complex Cp 2 Ru 2 (µ-CH 2 )(SiR 3 ) 2 (CO) 2 (6) successively. Further reaction of 5 and 6 with HSiR 3 affords methane under milder conditions (120 °C, 12 h) compared to the methane formation from 1. Meanwhile complicated exchange processes are observed for the silylated µ-methylene species 5 and 6. The dynamic behavior of the hydrido-silyl species 5 giving a 1 H-NMR spectrum consistent with an apparent C s structure at ambient temperature has been analyzed in terms of a mechanism involving intramolecular H-and R 3 Si-group migration between the two ruthenium centers. It is also revealed that intramolecular exchange reaction of the hydride and µ-CH 2 atoms in 5 proceeds via the coordinatively unsaturated methyl intermediate Cp 2 Ru 2 (CH 3 )(SiR 3 )(CO) 2 (9). In addition to these intramolecular processes, the hydride, µ-CH 2 , and SiR 3 groups in 5 and 6 exchange with external HSiR 3 via replacement of the η 2 -bonded H 2 or HSiR 3 ligand in µ-methylene or µ-silylmethylene intermediates Cp 2 Ru 2 (µ-CHX)(µ-CO)(CO)(η 2 -H-Y) [X, Y ) H, SiR 3 (7), SiR 3 , H (18), SiR 3 , SiR 3 (16)] as confirmed by trapping experiments of 7 with L (CO, PPh 3 ) giving Cp 2 Ru 2 (µ-CHX)(µ-CO)(CO)(L) [X, L ) H, CO (1), H, PPh 3 (11), SiR 3 , CO (12), SiR 3 , PPh 3 (13)]. Hydrostannanes (HSnR 3 ) also react with 4, in a manner similar to the reaction with HSiR 3 , to give the hydrido-stannyl-µ-methylene intermediate Cp 2 Ru 2 (µ-CH 2 )(H)(SnR 3 )(CO) 2 ( 20) and the distannyl-µ-methylene complex Cp 2 Ru 2 (µ-CH 2 )(SnR 3 ) 2 (CO) 2 ( 21) successively (the stannyl analogues of 5 and 6, respectively). The intramolecular exchange processes (H T SnR 3 , H T µ-CH 2 ) are also observed for 20. But the HSnPh 3 adduct 20c is further converted to a mixture containing the µ-η 1 :η 2 -phenyl complex Cp 2 Ru 2 (µ-Ph)(SnCH 3 Ph 2 )(CO) 2 ( 22) and the bis(µ-stannylene) complex Cp 2 Ru 2 (µ-SnPh 2 ) 2 (CO) 2 ( 23) instead of 21c. The isolation of 22 supports viability of the methyl species (9). These results suggest that methane formation from 1 follows (i) CO dissociation, (ii) H-SiR 3 oxidative addition giving the hydrido-silyl-µ-methylene intermediate 5, (iii) equilibrium with the methyl intermediate 9, (iv) a second oxidative addition of H-SiR 3 , and (v) elimination of methane repeating reductive elimination from mono-and dinuclear hydrido-methyl intermediates 27 and 28. The...

Reversible Isomerization via Migration of SnPh3 in S2CPCy3-Bridged Heterobinuclear Compounds. X-ray Structures of [(CO)3Re(μ-S2CPCy3)Mo(SnPh3)(CO)3] and [(CO)3(Ph3Sn)Re(μ-S2CPCy3)Mo(CO)3]

“…Although there is some precedent of migration of stannyl groups from a metal to a cyclopentadienyl group, this is the first example, as far as we know, of a reversible migration of a stannyl group between two metals. There are two previous reports describing the migration of silyl groups from Fe to Pt (irreversible), in [FePt(μ-PPh 2 )(CO) 4 (PPh 3 )(SiR 3 )], and between two Ru atoms (reversible), in [Ru 2 (μ-CH 2 )Cp 2 (CO) 2 (H)(SiR 3 )] …”

Synthesis and Reactivity of Labile MeCN Adducts of Diruthenium Bis(μ-methylene) Species, Cp2Ru2(μ-CH2)2(CO)n(MeCN)2-n(n= 1, 2): Reaction with H Sources, H−X (X = SiR3, SnR3, H), and C−C Coupling with Alkynes and Diazoalkanes

“…In the latter system, olefinic products, including the μ-alkenyl complexes Cp 2 Ru 2 (μ-CHCR 2 )(μ-H)(CO) 2 , were obtained via efficient coupling between the methylene unit in 5 and the external alkylidene unit. In addition, the methylene ligand in 4 and 5 was found to be converted to methane upon treatment with hydrosilane, and the formation mechanism of methane was successfully analyzed by using 5 2 …”

Thermal Si−C Bond Cleavage of LRhH(SiAr3)(μ-H)(μ-Cl)RhH(SiAr3)L (Ar = C6H5, C6H4F-p; L = P(i-Pr)3) To Give LRhH(μ-SiAr3)(μ-SiAr2)(μ-Cl)RhHL Containing Symmetrically Bridging Triarylsilyl and Diarylsilylene Ligands

“…The exchange of the organosilyl ligand was also reported to occur in several other mononuclear and dinuclear transition metal complexes containing a M−Si bond. Dinuclear Fe and Ru complexes with bridging methylene and carbonyl ligands and a terminal triorganosilyl ligand undergo smooth silyl ligand exchange on addition of triorganosilane. 13d, Our previous study on the reaction of diarylsilane with mer -RhCl(H)(SiHAr 2 )(PMe 3 ) 3 established the facile exchange of the diarylsilyl ligand through reductive elimination of diarylsilane from the complex followed by its oxidative addition . Measurement of the equilibrium constants revealed the relative stability of the Rh−Si bond in the order Rh−SiH(C 6 H 4 F- p ) 2 > Rh−SiHPh 2 > Rh−SiH(C 6 H 4 Me- p ) 2 .…”