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

Abstract

The monoolefin complex Rh(acac)(cyclooctene)(PCy3) (1) reacts with HGeEt3 to give Rh(acac)H(GeEt3)(PCy3) (2). On treatment of 2 with methyl propiolate and phenylacetylene the complexes Rh(acac){η2-CH(GeEt3)CHR}(PCy3) (R = CO2Me (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 HSnPh3. The reaction leads to Rh(acac)H(SnPh3)(PCy3) (5). In the presence of methyl propiolate, phenylacetylene, and (trimethylsilyl)acetylene complex 5 affords the alkenyl compounds Rh(acac){(E)-CHCHR}(SnPh3)(PCy3) (R = CO2Me (6), Ph (7), SiMe3 (8)). Similarly, the reactions of 5 with diethyl acetylenedicarboxylate and diphenylacetylene yield Rh(acac)(CRCHR)(SnPh3)(PCy3) (R = CO2Et (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)-CHCHC(OH)(CH2)4CH2}(SnPh3)(PCy3) (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)-CHCHC(CH3)CH2}(SnPh3)(PCy3) (12), whereas in the presence of 1,1-diphenyl-2-propyn-1-ol complex 5 affords the allenyl derivative Rh(acac)(CHCCPh2)(SnPh3)(PCy3) (13).