The synthesis of a cationic binuclear iron complex containing the η 2-butatriene ligand and its reactions with oxygen nucleophiles

Abstract

The synthesis of the first complex containing the unsubstituted η 2-butatriene ligand [Fp 2(CH 2CCCH 2)] 2+ (PF − 6) 2 (IV) is accomplished in 50% yield by oxidation of FpCH 2CCCH 2Fp with trityl hexafluorophosphate. IV reacts with aqueous sodium hydroxide to afford CH 2CFpCOCH 3 (IX) and with aqueous sodium bicarbonate to yield a mixture of IX and CH 2CFpCOCH 2Fp (VIII). The binuclear allene complexes Fp +(CH 2CCXCH 2Fp) X =OAc, OPh, OPh- p-NO 2 are formed by the addition of the respective anions to IV. Ethylation of VIII with triethyloxonium hexafluorophosphate gives CH 2CFpC +(OEt)CH 2Fp. The major product resulting from the reaction between IV and methanol is η 3-(CH 3OCH 2CFpC(CO 2Me)CH 2)-η 5-C 5H 5(CO)Fe, (XIVa). Methoxide yields η 3-(CH 2CC(CO 2Me)CH 2)(CO)-η 5-C 5H 5Fe as the major product in addition to smaller yields of XIVa and the isolable cis and trans isomers (XVI and XVII) of [η 5-C 5H 5(CO)-η 2-1,2-(CH 2CHOMe)Fe][Fe(CO) 2-η 5-(C 5H 5)]. These isomers equilibrate above 100°C. Ethoxide and isopropoxide give similar results. In contrast, the only characterizable product obtained from the reaction between t-butoxide and IV was Fp 2.