Reactivity of the bis(pentafluorophenyl)boranes ClB(C6F5)2 and [HB(C6F5)2]n towards late transition metal reagents

Abstract

The reactivities of the highly electrophilic boranes ClB(C₆F₅)₂ (1) and [HB(C₆F₅)₂]_n (2) towards a range of organometallic reagents featuring metals from Groups 7–10 have been investigated. Salt elimination chemistry is observed between 1 and the nucleophilic anions [(η⁵-C₅R₅)Fe(CO)₂]⁻ (R = H or Me) and [Mn(CO)₅]⁻, leading to the generation of the novel boryl complexes (η⁵-C₅R₅)Fe(CO)₂B(C₆F₅)₂ [R = H (3) or Me (4)] and (OC)₅MnB(C₆F₅)₂ (5). Such systems are designed to probe the extent to which the strongly σ-donor boryl ligand can also act as a π-acceptor; a variety of spectroscopic, structural and computational probes imply that even with such strongly electron withdrawing boryl substituents, the π component of the metal–boron linkage is a relatively minor one. Similar reactivity is observed towards the hydridomanganese anion [(η⁵-C₅H₄Me)Mn(CO)₂H]⁻, generating a thermally labile product identified spectroscopically as (η⁵-C₅H₄Me)Mn(CO)₂(H)B(C₆F₅)₂ (6). Boranes 1 and 2 display different patterns of reactivity towards low-valent platinum and rhodium complexes than those demonstrated previously for less electrophilic reagents. Thus, reaction of 1 with (Ph₃P)₂Pt(H₂CCH₂) ultimately generates EtB(C₆F₅)₂ (10) as the major boron-containing product, together with cis-(Ph₃P)₂PtCl₂ and trans-(Ph₃P)₂Pt(C₆F₅)Cl (9). The cationic platinum hydride [(Ph₃P)₃PtH]⁺ is identified as an intermediate in the reaction pathway. Reaction of 2 with [(Ph₃P)₂Rh(µ-Cl)]₂, in toluene on the other hand, appears to proceed via ligand abstraction with both Ph₃P·HB(C₆F₅)₂ (11) and the arene rhodium(I) cation [(Ph₃P)₂Rh(η⁶-C₆H₅Me)]⁺ (14) ultimately being formed.