The reaction of KReO4 with L [2-(arylazo)-1-methylimidazole, with aryl = Ph (L1), C6H4Me-p (L2) or C6H4Cl-p (L3)] in concentrated HCl afforded [ReVL(O)Cl3] 1. Aromatic amines and PPh3 smoothly converted 1 into [ReVL(NR)Cl3] 2 and [ReIIIL(OPPh3)Cl3] 3 respectively. Treatment of 3 with PPh3 yielded [ReIIIL(PPh3)Cl3] 4. Complexes of type 3 and 4 display large paramagnetic shifts of 1H NMR lines which spread over ≈60 ppm. Structure determination of [ReL1(O)Cl3] 1a, [ReL2(NC6H4Me-p)Cl3] 2a, [ReL3(OPPh3)Cl3] 3c and [ReL3(PPh3)Cl3] 4c has revealed meridional geometry for all except 4c which is facial. In the latter Re-azo and Re-PPh3 back bonding is maximized. The metal atom is displaced away from the equatorial plane by ≈0.3 Å towards the oxo ligand in 1a and the imido ligand in 2a. The imidazole nitrogen is co-ordinated trans to oxo, imido, Ph3PO and chloride ligands in 1a, 2a, 3c and 4c, respectively. The azo N=N distance is lengthened by ≥0.05 Å as a result of direct (3c, 4c) or indirect (1a, 2a) Re-azo back bonding. Azo reduction potential values are consistent with the low-lying nature of the azo(π*) orbital. The metal reduction potentials follow the trends: ReVI-ReV, 1 > 2 (imido better donor than oxo); ReIV-ReIII, 4 > 3 (stabilization of t2 by ReIII-PPh3 back bonding).
|Original language||English (US)|
|Number of pages||7|
|Journal||Journal of the Chemical Society - Dalton Transactions|
|State||Published - Nov 7 1999|
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