Experimental and theoretical studies of highly fluxional TpRu(PPh3)"H2SiR3" complexes (Tp = hydridotris(pyrazolyl)borate)

Citation
Sm. Ng et al., Experimental and theoretical studies of highly fluxional TpRu(PPh3)"H2SiR3" complexes (Tp = hydridotris(pyrazolyl)borate), ORGANOMETAL, 18(13), 1999, pp. 2484-2490
Citations number
52
Categorie Soggetti
Organic Chemistry/Polymer Science
Journal title
ORGANOMETALLICS
ISSN journal
02767333 → ACNP
Volume
18
Issue
13
Year of publication
1999
Pages
2484 - 2490
Database
ISI
SICI code
0276-7333(19990621)18:13<2484:EATSOH>2.0.ZU;2-P
Abstract
Reactions of TpRuH(CH3CN)(PPh3) with free silanes HSiR3 (R-3 = Et-3, (EtO)( 3), Ph-3, HEt2, HPh2, and H2Ph) in THF yield the complexes TpRu(PPh3)(H)(et a(2)-HSiR3), the formulation of which is inferred from NMR spectroscopic da ta. The chemical equivalence of the two hydrogen atoms of TpRu(PPh3)(H)(eta (2)-HSiR3) down to -100 degrees C is attributed to rapid fluxionality betwe en the two, i.e., TpRu(PPh3)(H-a)(eta(2)-HbSiR3) reversible arrow TpRu(PPh3 )(H-b)(eta(2)-HaSiR3). Molecular orbital calculations at the B3LYP level ha ve been performed to investigate the stereochemistry and the interconversio n processes of various structural isomers for TpRu(PPh3)(H)(eta(2)-HSiR3). The results further support the existence of a eta(2)-silane formulation fo r these complexes. Two stable structures, with a nonclassical eta(2)-silane ligand, have been found. These two structural isomers are found to be in e quilibrium with a low reaction barrier (7.5 kcal/mol). The interconversion between the enantiomeric pair of the most stable structure has almost no re action barrier (0.5 kcal/mol). Together with the experimental findings, a m echanistic cycle is proposed. The complexes TpRu(PPh3)(H)(eta(2)-HSiR3) rea ct reversibly with pressurized H-2, CH3CN, and PPh3 to give TpRuH(Hz)(PPh3) , TpRuH(CH3CN)(PPh3), and TpRuH(PPh3)(2), respectively.