The 14-valence-electron monohydride OsH(SnPh 2 Cl)(P i Pr 3 ) 2 (a), generated from OsH 3 (SnPh 2 -Cl){η 2 -CH 2 dC(CH 3 )P i Pr 2 }(P i Pr 3 ) (1), activates a C(sp 2 )-H bond of 2-vinylpyridine, (E)-N-(phenylmethylene)-2-pyridinamine, and R,β-unsaturated ketones. The activation of 2-vinylpyridine affords the elongated dihydrogen (d H-H ) 1.41 Å) derivative Os(SnPh 2 Cl)(NC 5 H 4o-CHdCH)(η 2 -H 2 )(P i Pr 3 ) 2 (2) in equilibrium (∆H°) -2.5 ( 0.2 kcal mol -1 and ∆S°) -14.8( 1.0 cal mol -1 K -1 ) with the tautomer OsH(NC 5 H 4 -o-CHdCH)(HSnPh 2 Cl)(P i Pr 3 ) 2 (3), where the stannane is bonded to the transition metal by an Os-H-Sn three-center bond (J H-Sn ) 183 Hz). The activation of (E)-N-(phenylmethylene)-2-pyridinamine gives rise to Os(SnPh 2 -Cl)(NC 5 H 4 -o-NCPh)(η 2 -H 2 )(P i Pr 3 ) 2 (4; d H-H ) 1.32 Å), whereas the treatment of 1 with methyl vinyl ketone and benzylidenacetone leads to Os(SnPh 2 Cl){C(R)CHC(O)CH 3 }(η 2 -H 2 )(P i Pr 3 ) 2 (R ) H ( 5), Ph ( 6)), which show blocked rotation of the dihydrogen ligand (d H-H ) 1.45 ( 5), d H-H ) 1.42 (6) Å) on the NMR time scale (∆H q ) 11.7 ( 0.4 kcal mol -1 and ∆S q ) -1 ( 1 cal mol -1 K -1 (5), ∆H q ) 10.8 ( 0.5 kcal mol -1 and ∆S q ) 0.4 ( 1 cal mol -1 K -1 (6)). Complex 1 also reacts with benzylidenacetophenone. The reaction initially gives Os(SnPh 2 Cl){C(Ph)-CHC(O)Ph}(η 2 -H 2 )(P i Pr 3 ) 2 (7), which isomerizes into Os(SnPh 2 Cl){C 6 H 4 C(O)CHdCHPh}(η 2 -H 2 )(P i Pr 3 ) 2 (8), resulting from the o-CH activation of the PhCO aryl group. Complex 8 is other example of blocked rotation of the dihydrogen ligand (d H-H ) 1.45 Å) on the NMR time scale (∆H q ) 10.6 ( 0.6 kcal mol -1 and ∆S q ) -6.3 ( 1.5 cal mol -1 K -1 ). The structures of 2 and 5 have been determined by X-ray diffraction analysis.
The square-planar cis-dicarbonyl complex Ir(C 2 Ph)(CO) 2 (PCy 3 ) (1) reacts with ca. 1 equiv of HSiR 3 to give, in quantitative yield, the corresponding alkynyl-hydrido-silyl derivatives Ir(C 2 Ph)(H)(SiR 3 )(CO) 2 (PCy 3 ) (SiR 3 ) SiEt 3 (2), SiPh 3 (3), SiHPh 2 (4), and SiH 2 Ph (5)). The reactivity of the related tetrafluorobenzobarrelene compound Ir(C 2 Ph)(TFB)(PCy 3 ) (6) toward HSiR 3 has been also studied by NMR spectroscopy. The addition of ca. 2 equiv of HSiEt 3 to a benzene-d 6 solution of 6 affords IrH 2 (SiEt 3 )(TFB)(PCy 3 ) (7) and PhCtCSiEt 3 in a 1:1 molar ratio, while the reaction of 6 with ca. 1 equiv of HSiPh 3 yields, after 1 h and 30 min, IrH 2 -(SiPh 3 )(TFB)(PCy 3 ) (10, 8%), Ir{C(SiPh 3 )dCHPh}(TFB)(PCy 3 ) (11, 52%), and PhCtCSiPh 3 (8%). The addition of ca. 1 equiv of H 2 SiPh 2 to a benzene-d 6 solution of 6 leads, after 1 h, to IrH 2 {Si(C 2 Ph)Ph 2 }(TFB)(PCy 3 ) ( 12) in 90% yield. The alkynyl compounds 1 and 6 have been found to be active catalysts for the addition of triethylsilane to phenylacetylene. In all experiments, PhCHdCH 2 , PhCtCSiEt 3 , cis-PhCHdCH(SiEt 3 ), trans-PhCHdCH(SiEt 3 ), and Ph(SiEt 3 )CdCH 2 were obtained. On the basis of the results from the stoichiometric reactions together those from the catalytic experiments, reaction pathways for the formation of these silylate products are discussed.
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