Mononuclear (allenylidene)metal complexes of a d8 system: Synthesis and molecular structure of trans-[RhCl(=C=C=CRR′)(PiPr3)2]

Article abstract of DOI:10.1021/om00019a031

The reaction of [RhCl(PiPr₃)₂] (1) with 1-alkynols HC≡CCRR′OH leads to the formation of either (alkyne)- or (alkynyl)hydridorhodium complexes as the first isolable products. In toluene at room temperature (R = H, Me, R′ = Ph; R, R′ = C₁₂H₈) or on irradiation (R = R′ = iPr), the initially formed compounds smoothly rearrange to give the isomeric (vinylidene)rhodium derivatives trans-[RhCl(=C=CHCRR′OH)(PiPr₃)₂] (8-11). On treatment with alumina or traces of acid, compounds 8-11 eliminate water to give the four-coordinate rhodium allenylidenes trans-[RhCl(=C=C=CRR′)(PiPr₃)₂] (12, R = H, R′ = Ph; 13, R, R′ = C₁₂H₈) or a mixture of isomeric (allenylidene)- and (vinylvinylidene)metal complexes. These mixtures are converted upon reaction with acidic Al₂O₃ to give pure samples of trans-[RhCl(=C=CHC(Ph)=CH₂)-(PiPr₃)₂] (16) and trans-[RhCl(=C=CHC(iPr)=CMe₂)(PiPr₃)₂] (17) in nearly quantitative yields. From 1 and HC≡CCPh(o-Tol)OH, the complete series of (alkyne)-, (alkynyl)hydrido-, (vinylidene)-, and (allenylidene)rhodium compounds 18-21 has been prepared, and the molecular structure of trans-[RhCl(=C=C=CPh(o-Tol))(PiPr₃)₂] (21) has been determined. Crystallographic data: orthorhombic, space group Pca2₁ (No. 29), a = 17.804(4) ?, b = 10.891(1) ?, c = 17.934(5) ?, V = 3477(1) ?³, Z = 4. The Rh-C distance in 21 is somewhat longer than in related (vinylidene)rhodium complexes but is almost identical with that in rhodium carbenes.