Preparation of new ‘diazo’ complexes of manganese stabilised by phosphite ligands

A series of mono- and binuclear aryldiazene complexes [Mn(ArNNH)(CO)nP5−n]BPh4 and [{Mn(CO)nP5−n}2(μ-HNNArArNNH)](BPh4)2 [P=P(OMe)3, P(OEt)3 or P(OPh)3; Ar=C6H5, 4-CH3C6H4; ArAr=4,4′-C6H4C6H4, 4,4′-C6H4CH2C6H4; n=1, 2 or 3] were prepared by allowing hydride species MnH(CO)nP5−n to react with the appropriate aryldiazonium salts at −80°C. Characterisation of the complexes by IR and variable-temperature 1H-, 31P-, 15N-NMR spectra (with 15N isotopic substitution) are reported. Treatment of aryldiazene derivatives containing both the tricarbonyl Mn(CO)3P2 and the dicarbonyl Mn(CO)2P3 fragments with NEt3 affords the pentacoordinate dicarbonyl aryldiazenido Mn(ArN2)(CO)2P2 and [Mn(CO)2P2]2(μ-N2ArArN2) derivatives. Instead, the aryldiazene bonded to the monocarbonyl fragment Mn(CO)P4 is unreactive towards base and does not give aryldiazenido species. Hydrazine complexes [Mn(RNHNH2)(CO)nP5−n]BPh4 [R=H, CH3 or C6H5; P=P(OMe)3, P(OEt)3 or P(OPh)3; n=1, 2 or 3] were prepared by reacting hydride species MnH(CO)nP5−n first with Brønsted acid (HBF4 or CF3SO3H) and then with an excess of the appropriate hydrazine. The binuclear complex [{Mn(CO)3[P(OEt)3]2}2(μ-NH2NH2)](BPh4)2 was also prepared. Oxidation reactions of phenylhydrazine cations [Mn(C6H5NHNH2)(CO)nP5−n]+ with Pb(OAc)4 at −40°C give the phenyldiazene [Mn(C6H5NNH)(CO)nP5−n]+ derivatives, whereas the oxidation of methylhydrazine [Mn(CH3NHNH2)(CO)nP5−n]+ complexes allows the synthesis of the first methyldiazene [Mn(CH3NNH)(CO){P(OMe)3}4]BPh4 derivative of manganese.