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Unsymmetrical Dirhenium Complexes That Contain [Re2]6+ and [Re2]5+ Cores Complexed by Tridentate Ligands with P2O and P2N Donor Sets

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posted on 22.12.2001, 00:00 by Shan-Ming Kuang, Phillip E. Fanwick, Richard A. Walton
The quadruply bonded dirhenium(III) complex (n-Bu4N)2Re2Cl8 reacts with tridentate ligands that contain essentially planar P,O,P donor sets to afford the complexes Re2Cl63-L1) (3) (L1 = bis[2-(diphenylphosphino)phenyl]ether) and (n-Bu4N)[Re2Cl71-L2)] (4) (L2 = 4,6-bis(diphenylphosphino)dibenzofuran). Spectroscopic and electrochemical data support the unsymmetrical structure Cl4ReReCl23-L1) in the case of 3, while 4 contains monodentate P-bound L2; both complexes contain ReRe bonds. The synthon cis-Re2(μ-O2CCH3)2Cl4(H2O)2 reacts with ligands L1, L2, 2,6-bis(diphenylphosphinomethyl)pyridine (L3), bis[2-(diphenylphosphino)ethyl]amine (L4), and N,N-bis[2-(diphenylphosphino)ethyl]trimethylacetamide (L5) to give the paramagnetic complexes Re2(μ-O2CCH3)Cl43-Ln) (59) with Re bonds. The lability of the μ-acetato ligands in 59 has been demonstrated by the reactions of compounds 5 (n = 1) and 7 (n = 3) with 4-Ph2PC6H4CO2H, 2-Ph2PC6H4CO2H, and quinoline-4-carboxylic acid to give complexes 1012 (from 5) and 1315 (from 7), respectively. These products contain uncoordinated donor atoms that can be used to produce mixed-metal assemblies. Compounds 5 and 7 also react with terephthalic acid (1,4-C6H4(CO2H) to give [Re2Cl43-L1)]2(μ-O2CC6H4CO2) (16) and [Re2Cl43-L3)]2(μ-O2CC6H4CO2) (17) in which electronic coupling between the paramagnetic sets of dirhenium units is very weak. Single-crystal X-ray structure determinations have been carried out on complexes 58, 11, 12, and 1416.