Abstract The structures and bonding of the complexes TML2 and TML2+ with planar tetracoordinate carbons (TM = Cu, Ag and Au; L = C3H2BCH3 and C3Me2BCMe3) have been investigated using density functional theory M06 method, in which L are the derivatives of 2-borabicyclo[1.1.0]but-1(3)-ene. The lengths of Au–C and Ag–C bonds in AuL2 and AgL2 are longer than those of in TML2+, whereas the lengths of Cu–C bonds in TML2 are shorter than those of in TML2+. The NBO analyses of TML2 and TML2+ reveal that the Cu–C bonds in CuL2 are conjugated π bonds, whereas Ag–C and Au–C in TML2 (TM = Ag and Au) are σ bonds. The first electron transition energies of TML2+ result from the d–π transition, and the wavelengths are close to 260 nm. Theoretically, the variations of the Gibbs free energies of the reactions of Ag(C3H2BCH3)2+ and Ag(C3Me2BCMe3)2+ with (tht)AuBr indicate that the two reactions are thermodynamically favorable. We also theoretically obtained the stable Au(III) complexes (C3H2BCH3)2AuBr2+ and (C3Me2BCMe3)2AuBr2+ with planar tetracoordinate carbons from the reactions of Au(C3H2BCH3)2+ and Au(C3Me2BCMe3)2+ with CsBr3.