1:1:1 [(R3P)Cu(Tm)] (R = phenyl, cyclohexyl, m- and p-tolyl) or [(R ' Ph2P)Cu(Tm)] (R ' = methyl or ethyl) triorganophosphine copper(I) adducts, containing the anionic, potential S-3(-), face-capping ligand hydrotris(3-methyl-1-imidazolyl-2-thione)borate [Tm](-), were synthesised from K[Tm], CuCl and the corresponding P-donor. No phosphine adduct was obtained when tri-o-tolyl-, tribenzyl-phosphine, triphenylarsine and triphenylantimony were reacted with K[Tm] and CuCl, [Cu(Tm)](n) being the product obtained always, in strong excess of the phosphorus donor. The probably polynuclear [Cu(Tm)](n) is stable towards Hmimt (3-methyl-1-imidazoline-2-thione), NH3, CS2, H2O and CO; it reacts with pyridine (py) to yield the 1:1:1 adduct [(py)Cu(Tm)]. [Cu(Tm)](n) also reacts with H2O2 yielding the poorly soluble derivative [Cu(mimt)](n) upon breaking of the B-N bond in the azolyl-borate ligand. All of the complexes synthesised were characterised through analytical and spectral OR, H-1 and P-31 NMR) measurements. The solid-state structures of [(m-tolyl(3)P)Cu(Tm)] and [(p-tolyl(3)P)Cu(Tm)] show the copper atoms to be tetracoordinate with the donor [Tm] behaving as an S-3(-), face-capping ligand.