Further studies on the interconversion of large ring and cyclometallated complexes of rhodium, with the diphosphines Bu^t₂P(CH₂)₅PBu^t₂and Bu^t₂PCH₂CHCHCH₂PBu^t₂

Abstract

Improved routes to the fluxional cyclometallated hydride [[graphic omitted]But2)] are reported. Treatment of this hydride with carbon monoxide and sodium tetraphenylborate in methanol gives the fluxional salt [[graphic omitted]But2)][Bph4], together with a small amount of the 16-atom ring complex, trans-[Rh2Cl2(CO)2{But2P(CH2)5PBut2)2], more readily prepared by treating [Rh2Cl2(CO)4] with the diphosphine. This 16-atom ring complex exists as two rotamers in solution at 25 °C. Although [[graphic omitted]But2)] gives [[graphic omitted]But2)] with sodium propan-2-oxide and carbon monoxide on the other hand the corresponding complex [[graphic omitted]But2)] on similar treatment gives a complex mixture (probably containing rotamers of large-ring chelates). Treatment of [[graphic omitted]But2)] with MeNC and sodium propan-2-oxide also gives mixtures, probably containing large-ring chelates. Treatment of [[graphic omitted]But2)] with MeNC or ButNC in the presence of sodium tetraphenylborate or ammonium hexafluorophosphate gives 16-atom ring chelate salts [Rh2(CNR)4{But2P(CH2)5PBut2}2][anion]2 which can also be made by treating [Rh(CNR)4][anion] with the diphosphine. Rotation of trans-MeNC–Rh–CNMe moieties around P–Rh–P bonds has been studied by variable-temperature n.m.r. spectroscopy. The complex [Rh2(CNBut)4(But2PCH2CHCHCHCH2PBut2)2][PF6]2 has also been prepared. Treatment of the cyclooctene complex [Rh2Cl2(C8H14)4] with But2P(CH2)5PBut2 and MeNC or ButNC (1 mol per rhodium atom) gives 16-atom ring complexes of type [Rh2Cl2(CNR)2{But2P(CH2)5PBut2}2]. The complex [Rh2Cl2(CNMe)2{But2P(CH2)5PBut2}2] gives only one rotamer in solution in which the two rhodiums are chemically non-equivalent. The diphosphine But2PCH2CHCHCH2PBut2 reacts similarly with [Rh2Cl2(C8H14)4] and MeNC but also gives a small amount of another (unidentified) product. Infrared and 1H, 31P, and 103Rh n.m.r. data are given.