Intermetallic transfer of unsymmetrical borylene fragments: isolation of the second early-transition-metal terminal borylene complex and other rare species.

Transition metal borylene complexes of the type [(OC)5M[double bond, length as m-dash]BN(SiMe3)(tBu)] (M = Cr, Mo, W) have been synthesised by salt elimination of the corresponding dibromoborane and the dianionic metallates Na2[M(CO)5]. The borylene complexes have been characterised by multinuclear solution-state NMR spectroscopy and solid-state molecular structure determination. The group 6 borylene complexes can be used to effectively transfer the borylene ligand to other transition metal complexes by replacing one or two carbonyl ligands upon irradiation of the reaction mixture with UV light. This borylene transfer reaction led to the formation of new terminal and bridging borylene complexes which cannot be formed by the corresponding salt elimination reactions, including a rare example of a bis(terminal borylene) complex and only the second reported terminal borylene complex of an early transition metal (vanadium).

A Binuclear 1,1'-Bis(boratabenzene) Complex: Unprecedented Intramolecular Metal-Metal Communication through a B-B Bond.

We report the synthesis of the first 1,1'-bis(boratabenzene) species by tetrabromodiborane(4)-induced ring-expansion reactions of cobaltocene. Six equivalents of cobaltocene are required as the species plays the dual role of reagent and reductant to yield [{(η(5) -C5 H5 )Co}2 {µ:η(6) ,η(6) -(BC5 H5 )2 }]. The formally dianionic bis(boratabenzene) moiety with a boron-boron single bond can be viewed as a symmetric dimer of the parent boratabenzene anion as well as the first example of a diboron analogue of biphenyl. The solution electrochemistry of the bimetallic complex shows four stepwise redox events, indicating significant intramolecular interaction between the cobalt ions across the 1,1'-bis(boratabenzene) unit. The magnetic properties, as investigated by variable-temperature SQUID magnetometry, reveal weak intramolecular antiferromagnetic interactions. Density functional theory calculations support the experimental results and add insight into the various electronic states of the complex.

Platinum trans-Bis(borirene) complexes displaying coplanarity and communication across a platinum metal center.

Ambient-temperature photolysis of the aminoborylene complex [(OC)5 Cr=B=N(SiMe3 )2 ] in the presence of a series of trans-bis(alkynyl)platinum(II) precursors of the type trans-[Pt(CCAr)2 (PEt3 )2 ] (Ar=Ph, p-C6 H4 OMe, and p-C6 H4 CF3 ) successfully leads to twofold transfer of the borylene moiety [:B=N(SiMe3 )2 ] onto the alkyne functionalities. The alkynyl precursors and resultant bis(borirene)platinum(II) complexes formed are of the type trans-[Pt(B{=N(SiMe3 )2 }C=CAr)2 (PEt3 )2 ] (Ar=Ph, p-C6 H4 OMe, and p-C6 H4 CF3 ). These species have all been successfully characterized by NMR, IR, and UV/Vis spectroscopy as well as by elemental analysis. Single-crystal X-ray diffraction has verified that these trans-bis(borirene)platinum(II) complexes display coplanarity between the twin three-membered rings across the platinum core in the solid state and stand as the first examples of coplanar conformations of twin borirene systems. These complexes were modeled using density functional theory (DFT), providing information helpful in determining the ability of the transition metal core to interact with each individual borirene ring system and allowing for the observed coplanarity of these rings in the solid state. This proposed transition metal interaction with the twin borirene systems is manifested in the electronic characterization of these borirene species, which display divergent photophysical UV/Vis spectroscopic profiles compared to a previously published mono(borirene)platinum(II) complex.