Organometallic chemistry of ethynyl boronic acid MIDA ester, HCCB(O 2 CCH 2 ) 2 NMe

The reactions of HCCBMIDA (BMIDA = B(O 2 CCH 2 ) 2 NMe) 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(S 2 CNR 2 )(CO)(PPh 3 ) 2 ] (R = Me, Et) and [Ru(CO) 2 (PPh 3 ) 3 ] afford the alkynyl complexes [Ru(CCBMIDA)(S 2 CNR 2 )(CO)(PPh 3 ) 2 ] and [RuH(CCBMIDA)(CO) 2 (PPh 3 ) 2 ], the latter being converted to [Ru(CCBMIDA)Cl(CO) 2 (PPh 3 ) 2 ] on treatment with chloroform. With [RuCl(dppe) 2 ]PF 6 the vinylidene salt [RuCl(CCHBMIDA)(dppe) 2 ]PF 6 is obtained, which reacts with Et 3 N to afford the neutral alkynyl derivative [Ru(CCBMIDA)Cl(dppe) 2 ]. Hydrometallation of HCCBMIDA by [RuHCl(CO)(PPh 3 ) 3 ] affords the coordinatively unsaturated σ-alkenyl complex [RuCl(CHCHBMIDA)(CO)(PPh 3 ) 2 ] which in turn reacts with CO, CNC 6 H 2 Me 3 -2,4,6, [Et 2 NH 2 ][S 2 CNEt 2 ] or K[HB(pz) 3 ] (pz = pyrazol-1-yl) to afford the coordinatively saturated complexes [Ru(CHCHBMIDA)Cl(CO) 2 (PPh 3 ) 2 ], [Ru(CHCHBMIDA)Cl(CO)(CNC 6 H 2 Me 3 )(PPh 3 ) 2 ], [Ru(CHCHBMIDA)(S 2 CNEt 2 )(CO)-(PPh 3 ) 2 ] and [Ru(CHCHBMIDA)(CO)(PPh 3 ){HB(pz) 3 }]. In all cases, the transannular N→B dative bond is retained in the BMIDA substituent.