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Homo- and heterodinuclear complexes of the tetrakis(pyrazolyl)borate ligand

Hallett, Andrew Jon, Adams, Christopher J., Anderson, Kirsty M., Baber, R. Angharad, Connelly, Neil G. and Prime, Christopher J. 2010. Homo- and heterodinuclear complexes of the tetrakis(pyrazolyl)borate ligand. Dalton Transactions 39 (25) , pp. 5899-5907. 10.1039/C0DT00044B

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Monometallic complexes of the tetrakis(pyrazolyl)borate ligand [ML2{B(pz)4}] {M = Rh, Ir; L2 = η-cod, η-nbd, (CO)2, (CO)(PPh3)} have two free pyrazolyl rings which can be coordinated to a second ML2 unit to give the dimeric compounds [L2M{μ-B(pz)4}ML2]+, and to a metal halide to give heterobimetallic species [L2M{μ-B(pz)4}M′Cl2]. 1H NMR spectroscopy shows that [(η-cod)Rh{μ-B(pz)4}Rh(η-cod)]+1+, [(η-nbd)Rh{μ-B(pz)4}Rh(η-nbd)]+2+, [(η-cod)Ir{μ-B(pz)4}Ir(η-cod)]+3+ and [(CO)2Rh{μ-B(pz)4}Rh(CO)2]+4+ are fluxional at room temperature. Cooling a solution of [(η-cod)Rh{μ-B(pz)4}Rh(η-cod)]+1+ to −90 °C slows the fluxional process, which involves inversion of the two B-(N–N)2-M six-membered rings. Attempts to synthesise the asymmetric complexes [(η-cod)Rh{μ-B(pz)4}Rh(η-nbd)]+7+, [(η-cod)Rh{μ-B(pz)4}Ir(η-cod)]+8+ and [(η-cod)Rh{μ-B(pz)4}Rh(CO)2]+9+ produced a mixture of [L2M{μ-B(pz)4}ML2]+, [L′2M′{μ-B(pz)4}M′L′2]+ and the desired species. The heterobimetallic complexes [L2Rh{μ-B(pz)4}M′Cl2] (M′ = Co, L2 = η-cod 10; M′ = Co, L2 = η-nbd 11; M′ = Co, L = CO 12; M′ = Co, L2 = (CO)(PPh3)13; M′ = Zn, L2 = η-cod 14; M′ = Zn, L2 = η-nbd 15; M′ = Pd, L2 = η-cod 16) possess square planar Rh(I) linked to square planar Pd(II) or tetrahedral Zn(II) and Co(II) centres. The paramagnetic Co(II) complexes give 1H NMR spectra with signals shifted over a range of 75 ppm. The UV-Vis spectra of 10–13 show four bands, one MLCT at Rh and three d-d transitions arising from the spltting of the 4T1(P) excited state due to approximate C2v symmetry at Co.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Chemistry
Subjects: Q Science > QD Chemistry
Publisher: RSC
ISSN: 1477-9226
Last Modified: 19 Mar 2016 22:15

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