Organometallic chemistry of ethynyl boronic acid MIDA ester, HC≡CB(O2CCH2)2NMe.

The reactions of HC≡CBMIDA (BMIDA = B(O2CCH2)2NMe) with a range of ruthenium complexes afford the first isolated examples of σ-alkynyl, σ-alkenyl and vinylidene complexes bearing 4-coordinate boron substituents. Specifically, the reactions of HC≡CBMIDA with [RuH(S2CNR2)(CO)(PPh3)2] (R = Me, Et) and [Ru(CO)2(PPh3)3] afford the alkynyl complexes [Ru(C≡CBMIDA)(S2CNR2)(CO)(PPh3)2] and [RuH(C≡CBMIDA)(CO)2(PPh3)2], the latter being converted to [Ru(C≡CBMIDA)Cl(CO)2(PPh3)2] on treatment with chloroform. With [RuCl(dppe)2]PF6 the vinylidene salt [RuCl(=C=CHBMIDA)(dppe)2]PF6 is obtained, which reacts with Et3N to afford the neutral alkynyl derivative [Ru(C≡CBMIDA)Cl(dppe)2]. Hydrometallation of HC≡CBMIDA by [RuHCl(CO)(PPh3)3] affords the coordinatively unsaturated σ-alkenyl complex [RuCl(CH=CHBMIDA)(CO)(PPh3)2] which in turn reacts with CO, CNC6H2Me3-2,4,6, [Et2NH2][S2CNEt2] or K[HB(pz)3] (pz = pyrazol-1-yl) to afford the coordinatively saturated complexes [Ru(CH=CHBMIDA)Cl(CO)2(PPh3)2], [Ru(CH=CHBMIDA)Cl(CO)(CNC6H2Me3)(PPh3)2], [Ru(CH=CHBMIDA)(S2CNEt2)(CO)-(PPh3)2] and [Ru(CH=CHBMIDA)(CO)(PPh3){HB(pz)3}]. In all cases, the transannular N→B dative bond is retained in the BMIDA substituent.