The preparation, structures, and reactions of the metallacyclobutenyl complexes [M3{C3R1R22}2X2] derived from addition of triarylcyclopro-penium salts to zerovalent palladium and platinum compounds
Abstract
Reaction of [M2(dba)3(CHCI3)](M = Pd or Pt; dba = PhCH![[double bond, length half m-dash]](https://www.rsc.org/images/entities/char_e006.gif)
CHCOCHCHPh) with [C3R1R22] Br gave [M3(C3R1R22)2Br2](M = Pd, R1= R2= Ph; M = Pd, Pt, R1= R2=p-MeOC6H4; M = Pd or Pt. R1= Ph, R2=p-MeOC6H4), which reacted with Tl(acac) to give the corresponding [M3(C3R1R22)2(acac)2][acac = pentane-2,5-dionato]. The platinum complex [Pt3{C3(p-MeOC6H4)3}2Br2] was also converted into [Pt3{C3(p-MeOC6H4)3}2(η5-C5H5)2]. [Pt3{C3(p-MeOC6H4)3}2(S2CNPr12)2]. and [Pt3{C3(p-MeOC6H4)3}2(L2)2]-[PF6]2[L = PPh3, L2= cycle-octa-1,5-diene (cod), bipyridyl, or o-phenanthroline]. The n.m.r. spectra showed that the unusual structure, which had been determined for [Pd3{C3Ph(p-MeOC6H4)2}2(acac)2], was present in all the other complexes, and that they each possessed a bent trimetallic framework composed of two metallacyclo-butenyl units {M(C3R1R22)} each π4-bonded to the central metal, each terminal metal bearing in addition acac, C5H5, S2CNPr12, or L2 ligands. The complexes exhibited dynamic behaviour in solution and ΔG‡ values were determined from the n.m.r. spectra. The process involves a racemisation about the central metal atom and may also be viewed as arising from a movement of the two metallacyclobutenyl units with respect to each other between two equivalent positions about the central metal atom.
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