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

Blagg, Robin J., Connelly, Neil G., Haddow, Mairi F., Hamilton, Alex, Lusi, Matteo, Orpen, A. Guy and Ridgway, Benjamin M. (2010) Isomerism in rhodium(I) N,S-donor heteroscorpionates: ring substituent and ancillary ligand effects. Dalton Transactions, 39 (48). pp. 11616-11627. ISSN 1477-9226

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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.

Item Type: Article
Faculty \ School: Faculty of Science > School of Chemistry
Depositing User: Pure Connector
Date Deposited: 14 Mar 2014 12:32
Last Modified: 24 Oct 2022 06:12
DOI: 10.1039/c0dt00774a

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