Isolation of ionic products in the reaction of CO2 with (tetrahydroborato)copper(I) complexes: synthesia and reactions of [(biL)(Ph3P)2Cu][HB(O2CH)3] and [(biL)(Ph3P)2Cu][H2B(O2CH)2] (biL=1,10-phenantroline, 3,4,7,8-tetramethyl-1,10-phenantroline).

Carbon dioxide reacts with the (tetrahydroborato)copper(I) complexes (biL)(Ph3P)Cu(BH4) (biL = 1,10-phenanthroline (phen) (1), 3,4,7,8-tetramethyl-1,10-phenanthroline (TMP) (2)) in the presence of free triphenylphosphine. In nonprotic solvents the stable crystalline complexes of formula [(biL)(Ph3P)2Cu][HB(O2CH)3] (biL = phen (3)) and [(biL)(Ph3P)2Cu][H2B(O2CH) 2] (biL = phen (4a), TMP (4b)) can be isolated. The related reactions of 1 with 13CO2 give the corresponding 13C-labeled products; the reaction of (TMP)(Ph3P)Cu(BD4) with CO2 leads to the deuterated derivatives. In protic solvents, CO2 reacts with 1 or 2, allowing the isolation of the covalent formato complexes (biL)(Ph3P)Cu(O2CH) (biL = phen (5a), TMP (5b)). These can be also obtained by heating 3, 4a, and 4b in ethanol, suggesting that these ionic formato - hydroborato species probably act as intermediates in the reducing property of BH4 toward carbon dioxide. The reactions of 4b with HBF4 and NaBPh4 give the ionic derivatives [(TMP)(Ph3P)2Cu](BF4) and [(TMP)(Ph3P)2Cu](BPh4). Complexes 3 and 4a have been confirmed to undergo a reversible interconversion. Infrared and multinuclear magnetic resonance data (1H, 11B, and 13C) strongly support the presence of the [HB(O2CH)3]- and [H2B(O2CH)2]- anions in the complexes 3, 4a, and 4b. In particular their 11B NMR spectra substantiate the existence of the BH and BH2 groups in these ionic products.