Syntheses and structural characterisation of [Ir4(CO)11(η1-L)] and [Ir4(CO)10(η1-L)2]{L =[Fe(η5-P3C2But2)(η5-P2C3But3)] and [Fe(η5-C5H5)(η5-P3C2But2)]} and [Ir4(CO)11{µ-η1 : η1-[Fe(η5-C5H5)(η5-P3C2But2)]}Ir4(CO)11] and its facile conversion to [Ir4H(CO)10{Fe(η5-C5H5)[η5-P3C(CMe2CH2)CBut]}Ir4(CO)11], via an unusual C–H activation

Abstract

The reactions of NBu₄[Ir₄(CO)₁₁Br]1 with equivalent amounts of [Fe(η⁵-P₃C₂Bu^t₂)(η⁵-P₂C₃Bu^t₃)] L¹ or [Fe(η⁵-C₅H₅)(η⁵-P₃C₂Bu^t₂)] L² in the presence of AgSbF₆ gave good yields of [Ir₄(CO)₁₁(η¹-L)]2a or 2b, besides [Ir₄(CO)₁₀(η¹-L)₂]3a and 3b, respectively, in which the ligands are bound via the P_A atom. The solid-state structure of 2b, established by an X-ray analysis, is that of the T_d-like isomer, although the low-temperature ³¹P-{¹H} NMR spectrum showed the presence of both C_3v- and T_d-like isomers in solution. Compound 2a underwent facile conversion to [Ir₄(CO)₁₀(µ-η²-L¹)]4avia CO loss and further interaction of the adjacent P_B atom of L¹. Compound 2b reacted with 1 in the presence of AgSbF₆ to yield [Ir₄(CO)₁₁(µ-η¹ : η¹-L²)Ir₄(CO)₁₁]5b, in which the second Ir₄ cluster was ligated via P_C, rather than P_B, according to NMR spectroscopy. This compound underwent clean conversion into [Ir₄H(CO)₁₀{Fe(η⁵-C₅H₅)[η⁵-P₃C(CMe₂CH₂)CBu^t]}Ir₄(CO)₁₁]6b,via CO loss and oxidative addition of a C–H bond of a tert-butyl substituent in the P₃C₂Bu^t₂ ring. The molecular structure of 6b was determined by a single crystal X-ray diffraction analysis, which showed that C–H activation occurred on the Ir₄ cluster bound via P_C.