The reactions of di-µ-methylene-bis(pentamethylcyclopentadienyl)-dirhodium(IV) complexes with benzylmagnesium chloride and with alkynylmagnesium chloride; X-ray structure of [(η5-C5Me5)Rh(CH2Ph)(µ-CH2)2Rh(η4-C5Me5CH2Ph)

Abstract

Reaction of trans-[(C5Me5)2Rh2(µ-CH2)2Cl2](1) with RCCMgCl gave trans-[(C5Me5)2Rh2(-µ-CH2)2(RC2)2](R = Ph or But). However attack on (1) by benzylmagnesium chloride occurred at one C5Me5 ring as well as at one rhodium to give [(η5-C5Me5)Rh(CH2Ph)(µ-CH2)2Rh(η4-C5Me5CH2Ph)](6). The structure of (6) has been deduced by n.m.r. spectroscopy and confirmed by a single-crystal X-ray structure determination which showed the two rhodiums [2.559(3)Å apart] to be linked by two µ-methylene bridges. One rhodium (oxidation state formally +4) bears a σ-benzyl and an η5-C5Me5 ring; the other rhodium (formally +2) is η4-bound to C5Me5CH2Ph where the benzyl on the C5 ring is exo to the metal. Reaction of [(C5Me5)2Rh2(η-CH2)2(MeCN)2][PF6]2 with R′CCH gave a complex [(C5Me5)2Rh2(µ-CH2CHCR′CHCR′CH)]PF6(7)(R′=p-chlorophenyl); on the basis of the n.m.r. spectra it is proposed that the two rhodiums are linked by a σ,σ,η5-CH2CHCR′CHCR′CH bridge. The mode of formation of these complexes is discussed.