Isomerism in rhodium(I) N,S-donor heteroscorpionates: ring substituent and ancillary ligand effects

Robin J. Blagg, Neil G. Connelly, Mairi F. Haddow, Alex Hamilton, Matteo Lusi, A. Guy Orpen, Benjamin M. Ridgway

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Abstract

The heteroscorpionate ligands [HB(taz)2(pzR)]− (pzR = pz, pzMe2, pzPh) and [HB(taz)(pz)2]−, synthesised from the appropriate potassium hydrotris(pyrazolyl)borate salt and 4-ethyl-3-methyl-5-thioxo-1,2,4-triazole (Htaz), react with [{Rh(cod)(μ-Cl)}2] to give [Rh(cod)Tx] {Tx = HB(taz)2(pz), HB(taz)2(pzMe2), HB(taz)2(pzPh), HB(taz)(pz)2}; the heteroscorpionate rhodaboratrane [Rh{B(taz)2(pzMe2)}{HB(taz)2(pzMe2)}] is the only isolable product from the reaction of [{Rh(nbd)(μ-Cl)}2] with K[HB(taz)2(pzMe2)]. Carbonylation of the cod complexes gave a mixture of [Rh(CO)2Tx] and [(RhTx)2(μ-CO)3] which reacts with PR3 to give [Rh(CO)(PR3)Tx] (R = Cy, NMe2, Ph, OPh). In the solid state the complexes are square planar with the particular structure dependent on the steric and/or electronic properties of the scorpionate and ancillary ligands. The complex [Rh(cod){HB(taz)(pz)2}] has the heteroscorpionate κ2[N2]-coordinated to rhodium with the B–H bond directed away from the rhodium square plane while [Rh(cod){HB(taz)2(pzMe2)}] is κ2[SN]-coordinated, with the B–H bond directed towards the metal. The complexes [Rh(CO)(PPh3){HB(taz)2(pz)}] and [Rh(CO)(PPh3){HB(taz)2(pzMe2)}] are also κ2[SN]-coordinated but with the pyrazolyl ring cis to PPh3; in the former the B–H bond is directed towards rhodium while in the latter the ring is pseudo-parallel to the rhodium square plane, as also found for [Rh(CO)2{HB(taz)2(pzMe2)}]. The analogues [Rh(CO)(PR3){HB(taz)2(pzMe2)}] (R = Cy, NMe2) have the phosphines trans to the pyrazolyl ring. Uniquely, [Rh(CO)(PPh3){HB(taz)2(pzPh)}] is κ2[S2]-coordinated. A qualitative mechanism is given for the rapid ring-exchange, and hence isomerisation, observed in solution.
Original languageEnglish
Pages (from-to)11616-11627
Number of pages12
JournalDalton Transactions
Volume39
Issue number48
DOIs
Publication statusPublished - 2010

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