title: Circumventing redox chemistry: synthesis of transition metal boryl complexes from a boryl nucleophile by decarbonylation.
abstract: The very strong reducing capabilities of the boryllithium nucleophile (THF)2Li{B(NDippCH)2} (1, Dipp = 2,6-iPr2C6H3) render impractical its use for the direct introduction of the {B(NDippCH)2} ligand via metathesis chemistry into the immediate coordination sphere of transition metals (d(n), with n ≠ 0 or 10). Instead, 1 typically reacts with metal halide, amide and hydrocarbyl electrophiles either via electron transfer or halide abstraction. Evidence for the formation of M-B bonds is obtained only in the case of the d(5) system [{(HCDippN)2B}Mn(THF)(μ-Br)]2. Lower oxidation state metal carbonyl complexes such as Fe(CO)5 and Cr(CO)6 react with 1 via nucleophilic attack at the carbonyl carbon atom to give boryl-functionalized Fischer carbene complexes Fe(CO)4{C(OLi(THF)3)B(NDippCH)2} and Cr(CO)5{C(OLi(THF)2)B(NDippCH)2}. Although C-to-M boryl transfer does not occur for these formally anionic systems, more labile charge neutral bora-acyl derivatives of the type LnM{C(O)B(NDippCH)2} [LnM = Mn(CO)5, Re(CO)5, CpFe(CO)2] can be synthesized, which cleanly lose CO to generate M-B bonds. From a mechanistic standpoint, an archetypal organometallic mode of reactivity, carbonyl extrusion, has thus been shown to be applicable to the boryl ligand class, with (13)C isotopic labeling studies confirming a dissociation/migration pathway. These proof-of-methodology synthetic studies can be extended beyond boryl complexes of the group 7 and 8 metals (for which a number of versatile synthetic routes already exist) to provide access to complexes of cobalt, which have hitherto proven only sporadically accessible.
authors.affiliation: Inorganic Chemistry Laboratory, Department of Chemistry, University of Oxford , South Parks Road, Oxford OX1 3QR, United Kingdom.
authors.forename: René
authors.initials: R
authors.lastname: Frank
authors.forename: James
authors.initials: J
authors.lastname: Howell
authors.forename: Rémi
authors.initials: R
authors.lastname: Tirfoin
authors.forename: Deepak
authors.initials: D
authors.lastname: Dange
authors.forename: Cameron
authors.initials: C
authors.lastname: Jones
authors.forename: D Michael P
authors.initials: DM
authors.lastname: Mingos
authors.forename: Simon
authors.initials: S
authors.lastname: Aldridge