Late-metal metallacyclobutenes: Synthesis, isolation, and reactivity studies of cobaltacyclobutenes

Cobaltacyclobutenes (η5-C₅H₅)(PPh ₃)Co[C(CO₂Et)=C(TMS)CH(CO₂Et)] and (η 5-C₅H₅)(PPh₃)Co[C(TMS)=C(CO ₂Et)CH(CO₂Et)] were synthesized by the treatment of (η 5-C₅H₅)(PPh₃)Co[η2-(CH ₃)₃SiC≡CCO₂Et] with ethyl diazoacetate. The newly synthesized cobaltacyclobutenes were structurally characterized. The thermal decomposition products of the aforementioned cobaltacyclobutenes were also isolated and structurally characterized. Furthermore, the isolation and characterization of the thermal decomposition products of cobaltacyclobutene (η5-C₅H₅)(PPh₃)Co[C(SO ₂Ph)=C(TMS)CH(CO₂Et)] were isolated and one of the products was also structurally characterized.; Cobalt-alkyne complexes (η5-C₅H₅)(PPh ₃)Co[η2-(CH₃)₃SiC≡CCO ₂Et], (η5-C₅H₅)(PPh₃)Co[η 2-(CH₃)₃SiC≡CCOCH₃], (η 5-C₅H₅)(PPh₃)Co[η2-(CO ₂Me)C≡C(CO₂Me)], and (η5-C ₉H₇)(PPh₃)Co[η2-(TMS)C≡C(SO ₂Ph)] were synthesized and structurally characterized. The previously reported thermal decomposition of cobalt-alkyne (η5-C ₅H₅)(PPh₃)Co[η2-(CO₂Me)C≡C(CO ₂Me)] was reinvestigated and found to actually generate an ortho-metallated vinyl-phosphonium complex (η5-C ₅H₅)Co[η2-(MeO₂C)HC=C(CO ₂Me)PPh₂(η1-o-C ₆H₄)] and a tricobalt bis(carbyne) cluster [(η 5-C₅H₅)Co]₃[μ 3,η3-CCO₂Me][μ3,η 3-CCO₂Me], both of which where structurally characterized.; A cobalt-mediated nitro reduction and oxygen atom transfer reaction was discovered by the conversion of (η5-C₅H ₅)Co(PPh₃)₂ and nitro compounds to give mononuclear η 1-(N)-nitrosoalky1 of the general composition (η 5-C₅H₅)Co(PPh₃){lcub}[η1-( N)]-N(O)R{rcub} and dinuclear μ-[η1-(N),η 2-(N,O)]-nitrosoaryl complexes of the composition [(η5-C₅H₅)Co]₂{lcub}μ-[η 1-(N),η2-(N,O)]-N(O)Ar{rcub} ₂.; The treatment of (η5-C₅H₅)Co(PPh ₃)₂ with an alkynylsulfoxide led to the discovery of a cobalt insertion reaction into the sulfur-carbon(sp) bond. The isolated product was found to be a rare cobalt-sulfenato complex (η5-C ₅H₅)Co(SOC₆H₄CH₃)(C≡CSi(CH ₃)₃)PPh₃ that was structurally characterized. The newly generated sulfenato complex could be oxidized to the corresponding sulfinato complex (η5-C₅H₅)Co(SO ₂C₆H₄CH₃)(C≡CSi(CH₃) ₃)PPh₃, which was also structu...