The thermal reduction of the copper(II) complexes [CuII(N2H4)3][B10H10]·nH2O (I·nH2O) and [CuII(NH3)4][B10H10]·nH2O (II·nH2O) has been studied in an argon atmosphere at 900 °C. It has been found that the annealing of both compounds results in a Cu@BN boron-containing copper composite. It has been shown that this process leads to the formation of a boron nitride matrix doped with cubic copper(0) nanoparticles due to the copper(II)→copper(I)→copper(0) thermal reduction. The phase composition of annealing products I900 and II900 has been determined based on powder X-ray diffraction, IR spectroscopy and thermal analysis data. The morphology, average particle size and composition of the composite have been determined by TEM and high-resolution TEM + EDS. The average particle size has been found to be about 81 nm and 52 nm for samples I900 and II900, respectively. Comparison of the results obtained using physicochemical studies has shown the identity of the composition of the products of annealing I900 and II900. The electrical properties of a coating based on an I900 sample modified with Cu0→Cu2O in situ during deposition on a chip at 300 °C in air have been studied. As a result, with increasing temperature, an increase in the electrical conductivity characteristic of semiconductors has been observed.