Metal carbene (M=C) complexes have proven highly useful because of their capacity to undergo metathesis reactions, which exchange the carbene group with another doubly bonded fragment. Recently, several different researchers have prepared boron analogs (M=B) of these compounds, with a double bond between a transition metal and a monovalent boron, or borylene, center.
Kays et al. have shown that one such compound undergoes metathesis, much like its carbon cousin. The borylene fragment, bearing a diisopropyl amino group, is bonded to an organometallic iron center. Room-temperature exposure of this compound to a solution of triphenylphosphine sulfide (Ph3P=S) quickly cleaves the P=S linkage, pairing the aminoborylene with the sulfur and leaving the phosphine coordinated to the iron. Similarly, treatment with triphenylarsine oxide (Ph3As=O) produces a boron oxide compound and an arsine-coordinated metal complex. The analogous reaction with triphenylphosphine oxide (Ph3P=O) is slow enough to permit isolation of an intermediate, which the authors characterized by x-ray crystallography. This intermediate shows a P-O-B linkage and lengthened Fe-B bond, suggesting that these reactions proceed by initial attack of the boron center by the electronegative oxygen or sulfur. -- JSY
Angew. Chem. Int. Ed. 10.1002/anie.200502343 (2005).
