The synthesis of di- and tetra-nuclear p-cymene–osmium hydride complexes; characterisation by 1H(187Os) reverse INEPT two-dimensional nuclear magnetic resonance spectroscopy

Abstract

[(p-MeC₆H₄CHMe₂)₂Os₂(µ-H)(µ-Cl)Cl₂] was formed from reaction of propan-2-ol with either [(p-MeC₆H₄CHMe₂)₂Os₂Cl₄](in the presence of KPF₆ or HPF₆ as catalyst) or [(p-MeC₆H₄CHMe₂)₂Os₂(µ-Cl)₃][PF₆]. The dinuclear trihydride [(p-MeC₆H₄CHMe₂)₂Os₂(µ-H)₃]⁺(5) and the tetranuclear tetrahydride [(p-MeC₆H₄CHMe₂)₄Os₄(µ-H)₄]²⁺ were obtained from reaction of [(p-MeC₆H₄CHMe₂)₂Os₂(µ-OH)₃]⁺(4) with propan-2-ol, and the trihydride (5) was also prepared by reaction of (4) with formaldehyde. The chloro-acetate [(p-MeC₆H₄CHMe₂)Os(O₂CMe)Cl] gave a mixture of [(p-MeC₆H₄CHMe₂)₂Os₂(µ-H)(µ-Cl)-(µ-O₂CMe)]⁺ and [(p-MeC₆H₄CHMe₂)Os₂(µ-H)₂(µ-O₂CMe)]⁺(13); while the diacetate [(p-MeC₆H₄CHMe₂)Os(O₂CMe)₂](8a) gave a mixture of (13), [(p-MeC₆H₄CHMe₂)₂Os₂(µ-H)-(µ-O₂CMe)₂]⁺(14), and (5) on reaction with propan-2-ol at 80 °C. The bis(trifluoroacetate)[(p-MeC₆H₄CHMe₂)Os (O₂CCF₃)₂] reacted analogously with propan-2-ol to give a mixture of two neutral complexes, [(p-MeC₆H₄CHMe₂)₂Os₂(µ-H)(µ-O₂CCF₃)(O₂CCF₃)₂] and [(p-MeC₆H₄CHMe₂)₂Os₂(µ-H)₂(O₂CCF₃)₂]. In each reaction the proportions of each product depended on the time of reaction, longer times favouring more highly hydrided complexes. The new hydride complexes were characterised with the help of n.m.r. spectroscopy including ¹H(¹⁸⁷Os) reverse INEPT two-dimensional n.m.r. spectra. The diacetate (8a) underwent hydrolysis to give [(p-MeC₆H₄CHMe₂)₂Os₂(µ-OH)₂(µ-O₂CMe)]⁺ and methanolysis to give [(p-MeC₆H₄CHMe₂)₂Os₂-(µ-OMe)₃]⁺, and on work-up (14) was hydrolysed to [(p-MeC₆H₄CHMe₂)₂Os₂(µ-H)(µ-OH)-(µ-O₂CMe)₂].