CHEMISTRY OF COBALT COMPLEXES WITH 1,2-BIS-(DIETHYLPHOSPHINO)ETHANE - HYDRIDES, CARBON-DISULFIDE COMPLEXES, AND C-H CLEAVAGE IN ACTIVATED ALK-1-YNES - CRYSTAL-STRUCTURE OF [COH(CCCO2ET)(ET2PCH2CH2PET2)2]-[BPH4]

The reaction of anhydrous CoCl2 with depe [1,2-bis(diethylphosphino)ethane] yields [CoCl2(depe)2] 1, which reacts with Na[BPh4] in ethanol to give five-co-ordinate [CoCl(depe)2][BPh4] 2. Both complexes have been studied by EPR spectroscopy. Complex 1 reacts with NaBH4 in ethanol yielding [CoH2(depe)2]+, isolable as the tetraphenylborate salt 3. This compound is stereochemically non-rigid in solution, having a cis configuration at low temperatures. The spin-lattice relaxation times (T1) for the hydrides of 3 suggest a classical formulation for this complex. The monohydride [CoH(depe)2] 4 is obtained by deprotonation of 3 using KOBu(t). Complex 3 reacts with CO and CS2 with reductive elimination of H-2, yielding (Co(CO) (depe)2] [BPh4] 5 and [Co(eta2-CS2) (depe)2] [BPh4] 6, respectively, both stereochemically non-rigid in solution. The reaction of 6 with alkyl halides leads to CS2 elimination, and formation of [CoX(depe)2] [BPh4] derivatives (X = Br 7 or 1 8). Complex 6 reacts with activated alk-1-ynes eliminating CS2 and undergoing an oxidative addition of the alkyne, yielding the hydridoalkynyl complexes [CoH(C=CR)(depe)2][BPh4] (R = Ph 9 or CO2Et 10). A mechanistic study of the reaction between 6 and HC=CCO2Et has been carried out, and the X-ray crystal structure of 10 determined.