Bora‐alkenes: Metal Coordination and Reactions with BH‐boranes

Abstract

The neutral N‐heterocyclic carbene stabilized bora‐alkene 1, conveniently prepared by a BH borenium/hydroboration route, forms stable copper, gold or palladium π‐complexes. The polar bora‐alkene B=C system undergoes regioselective hydroboration reactions with the (C6F5)2BH or C6F5BH2 ⋅ SMe2 boranes. The latter reaction involves a subsequent rearrangement that leads to internal hydride vs. isothiocyanate substituent exchange at the borane pair.

Borataalkenes, boraalkenes, and the η2-B,C coordination mode in coordination chemistry and catalysis

“…Erker subsequently reported the synthesis of a series of boraalkene complexes derived from NCS-substituted boraalkene 87 (Scheme 23). 8 Complexation with group 11 metal precursors yield η 2 -B,C boraalkene complexes 88 and 89 . In both complexes the metal–carbon bond distance is significantly shorter than the metal–boron distance.…”

“…Besides borataalkenes, several other ligand motifs feature η 2 -B,C binding, namely boraalkenes, 7,8 arylboranes (ambiphilic ligands) and borylferrocenes (Fig. 3).…”

The BC bond: some recent developments

“…Similarly, the isothiocyanato containing boraalkene 42 formed stable copper, gold, or palladium π-complexes 53 with CuCl, AuCl(SMe 2 ), or [(C 3 H 5 )PdCl] 2 reagents, respectively (Scheme 10a). 30 The related Fe(CO) 4 complex 54 was obtained from the reaction of Nöth's boraalkene 31a with Fe 2 (CO) 9 . 31 The NHC-stabilized borabutadiene 51 reacted with the bis (ethylene)RhCl dimer to give the dimeric (η 4 -borabutadiene) RhCl complex 55 (characterized by X-ray diffraction), which subsequently underwent an intramolecular C-H activation reaction to a mixture of η 3 -methyl-boraallyl Rh complex isomers 56 (Scheme 10b).…”

“…Similarly, the isothiocyanato containing boraalkene 42 formed stable copper, gold, or palladium π-complexes 53 with CuCl, AuCl(SMe 2 ), or [(C 3 H 5 )PdCl] 2 reagents, respectively (Scheme 10a). 30 The related Fe(CO) 4 complex 54 was obtained from the reaction of Nöth's boraalkene 31a with Fe 2 (CO) 9 . 31…”

π-Bonding of Group 11 Metals to a Tantalum Alkylidyne Alkyl Complex Promotes Unusual Tautomerism to Bis-alkylidene and CO2 to Ketenyl Transformation

“…The π-activation of unsaturated hydrocarbons, such as alkenes, dienes, alkynes, or allenes, via coinage metals is well-established − and led to numerous methodologies and applications, especially in organic chemistry and catalysis. − Coinage metals are also known to efficiently coordinate to a number of heteroelement-based π-systems, − yet practical applications of the latter still remain limited. Despite the interest of metal–carbon triple bonds in organometallic chemistry, − the activation of MC motifs via external d-block metal centers is still in its infancy.…”