The structures of the synthetically useful Cu(I) compounds [Tp t-Bu,MeCu 1] 2·0.5toluene ( 1) (C 51.5H 84B 2Cu 2N 12, a = 13.2425(2), b = 13.9201(2), c = 17.6033(3) A ̊ , α = 105.137(1), β = 106.730(1), γ = 103.548(1)°, V = 2826.73(8) A ̊ 3 , triclinic, P l , Z = 2) ( Tp R,R′ =[ HB(3- R,5- R′pz) 3] ; pz = pyrazoly) and [Tp t-Bu,i-PrCu 1] 2 ( 2) (C 60H 104B 2Cu 2N 12, a = 23.3168(2), b = 14.3594(2), c = 20.2819(2) A ̊ , β = 99.05(1)°, V = 6706.2(1) A ̊ 3 , monoclinic, P2 1/ c, Z = 4) have been examined by X-ray analysis as well as by IR and NMR to reveal a complex pattern of BH…Cu interactions that persist in solution. As opposed to the structures of the pseudo-tetrahedral carbonyl adducts [Tp t-Bu,MeCu(CO)] ( 3) (C 25H 40BCuN 6O, a = 15.502(4), b = 9.681(2), c = 19.049(6) A ̊ , β = 95.94(2)°, V = 2843(1) A ̊ 3 , monoclinic, Pc, Z = 4) and [Tp t-Bu,i-PrCu(CO)] ( 4), the structure of 1 and 2 display an ‘inverted’ configuration at the boron atom that directs the BH units towards the dicopper(I) core at a position suitable for a three-center, two-electron BH…Cu bonding interaction.