Synthesis of Rh(acac)H(GeEt3)(PCy3) and Rh(acac)H(SnPh3)(PCy3) and Their Reactions with Alkynes

The monoolefin complex Rh(acac)(cyclooctene)(PCy 3 ) ( 1 ) reacts with HGeEt 3 to give Rh(acac)H(GeEt 3 )(PCy 3 ) ( 2 ). On treatment of 2 with methyl propiolate and phenylacetylene the complexes Rh(acac){η 2 -CH(GeEt 3 ) CHR}(PCy 3 ) (R = CO 2 Me ( 3 ), Ph ( 4 )) are obtained. The X-ray crystal structure analysis of 3 reveals that the coordination geometry around the rhodium center is almost square-planar with the olefin disposed perpendicular to the coordination plane of the rhodium atom. Complex 1 also reacts with HSnPh 3 . The reaction leads to Rh(acac)H(SnPh 3 )(PCy 3 ) ( 5 ). In the presence of methyl propiolate, phenylacetylene, and (trimethylsilyl)acetylene complex 5 affords the alkenyl compounds Rh(acac){( E )-CH CHR}(SnPh 3 )(PCy 3 ) (R = CO 2 Me ( 6 ), Ph ( 7 ), SiMe 3 ( 8 )). Similarly, the reactions of 5 with diethyl acetylenedicarboxylate and diphenylacetylene yield Rh(acac)(CR CHR)(SnPh 3 )(PCy 3 ) (R = CO 2 Et ( 9 ), Ph ( 10 )). The addition of 1 equiv of 1-ethynyl-1-cyclohexanol to a pentane suspension of 5 leads to the hydroxyalkenyl derivative Rh(acac){( E )-CH CHC(OH)(CH 2 ) 4 CH 2 }(SnPh 3 )(PCy 3 ) ( 11 ). The structure of 11 was determined by X-ray analysis. The coordination geometry around the metal center can be rationalized as a square pyramid with the stannyl ligand in the apical position. Although the hydroxyalkenyl ligand of 11 is stable and does not dehydrate to give the corresponding α,β-unsaturated alkenyl compound, complexes of this type can be prepared from enynes. Thus, the reaction of 5 with 2-methyl-1-buten-3-yne leads to the α,β-unsaturated alkenyl complex Rh(acac){( E )-CH CHC(CH 3 ) CH 2 }(SnPh 3 )(PCy 3 ) ( 12 ), whereas in the presence of 1,1-diphenyl-2-propyn-1-ol complex 5 affords the allenyl derivative Rh(acac)(CH C CPh 2 )(SnPh 3 )(PCy 3 ) ( 13 ).