Rhenium Nitrosyl Complexes Bearing Large-Bite-Angle Diphosphines

A series of [ReBr2(MeCN)(NO)(P∩P)] complexes (P∩P = 1,1′-bis(diphenylphosphino)ferrocene (dppfc) (1a), 1,1′-bis(diisopropylphosphino)ferrocene (diprpfc) (1b), 2,2′-bis(diphenylphosphino)diphenyl ether (dpephos) (1c), 10,11-dihydro-4,5-bis(diphenylphosphino)dibenzo[b,f]oxepine (homoxantphos) (1d), 4,6-bis(diphenylphosphino)-10,10-dimethylphenoxasilin (Sixantphos) (1e)) were prepared with diphosphines varying in the P–Re–P bite angles. 1a,c–e were obtained from the reaction of [ReBr5(NO)][NEt4]2 with an excess of the respective diphosphine in MeCN or MeCN/THF mixtures at elevated temperatures. Compound 1b was obtained by an alternative route, cleaving the dinuclear [{ReBr(μ2-Br)(NO)(diprpfc)}2] unit (2b) with MeCN. 2b was prepared from the reaction of [ReBr5(NO)][NEt4]2 with diprpfc in EtOH. The reaction of 1a–d with HSiEt3 gave the seven-coordinate [ReBr(H)2(SiEt3)(NO)(P∩P)] compounds 4a–d, of which 4a,c,d are only stable in solution in the presence of HSiEt3. The SiMe3 (4f) and SiCl3 (4g) derivatives of 4b were also prepared by applying the reaction of 1b with HSiMe3 and HSiCl3. 1a,c,e, 2b, and 4f,g were structurally characterized. For 1c,e, 2b, and 4f,g NO/Br disorder was observed, which originates from the presence of two isomeric forms in the crystals of the respective compounds. For 1c,d fast interconversion of these isomers could be observed in their 31P{1H} NMR spectra at room temperature.