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Kinetic studies were performed for the chelate ring closing and opening process of cyclopentadienyl cobalt(III) complexes having a pendant N-functional group with an amine, piperidine or pyridine moiety in the side chain. The metal–nitrogen bond energy was measured. The rate of chelation by such pendant N-functionalized side chains in diiodomonocarbonyl cobalt(III) reaction intermediates is determined by the electronic density on the donor atom and the strength of the forming chelated bond. The steric factor around the donor atom plays a secondary role. On the basis of the enthalpies and entropies obtained from the kinetic studies, the process of chelate ring closing in diiodomonocarbonyl cobalt(III) reaction intermediates is via an associative pathway involving loss of CO, while the chelate ring opening process in the resulted chelators is via a metal–nitrogen bond cleavage, solvation then metal–phosphorus bond formation pathway during substitution of PPh 3 . The chelator with the most rigid arm of picolyl shows a smallest steric hindrance for incoming PPh 3 compared to the other two analogues.

Cobaltocene [η 5 -C 5 H 4 COOC(CH 3 )CH 2 ] 2 Co ( 1 ) was synthesized from CoCl 2 ·6H 2 O at −30 °C. 1 showed two reversible redox potentials at −0.335 and −1.418 V, respectively. It was found that the electron-withdrawing substituent on the cyclopentadienyl ligand facilitated the formation of cobaltocene quantitatively. (η 5 -C 5 H 4 COOCH 3 )Co(C 8 H 12 ) ( 2 ) was synthesized from 1 at −50 °C under sodium amalgam and the structure of 2 was determined by single-crystal X-ray diffraction. The change of the electron-withdrawing group from the carboisopropenyloxy to the carbomethoxy group on the cyclopentadienyl ligand is also discussed.

Chelates of the parent compounds ( η 5 -C 5 H 4 C(O)CH 2 OCH 3 )Mn(CO) 3 ( 1 ). ( η 5 -C 5 H 4 C(O)CH 2 SCH 3 )Mn(CO) 3 ( 2 ), ( η 5 -C 5 H 4 C(O)CH 2 CH 2 SCH 3 )Mn(CO) 3 ( 3 ), ( η 5 -C 5 H 4 CH 2 COOCH 3 )Mn(CO) 3 ( 4 ), and ( η 5 -C 5 H 4 C(O)CH 2 COOCH 3 )Mn(CO) 3 ( 5 ) were prepared by photolysis. Only the chelates ( η 1 : η 5 -C 5 H 4 C(O)CH 2 SCH 3 )Mn(CO) 2 ( 2chelate ) and ( η 1 : η 5 -C 5 H 4 C(O)CH 2 CH 2 SCH 3 )Mn(CO) 2 ( 3chelate ) were stable enough to be isolated. The X-ray structure of 2chelate was determined and demonstrated ring strain in the chelate ring. Derivatives of the chelates were obtained by thermal substitution of the chelated group. Substitution of the chelated groups in ( η 1 : η 5 -C 5 H 4 C(O)CH 2 OCH 3 )Mn(CO) 2 ( 1chelate ), ( η 1 : η 5 -C 5 H 4 CH 2 COOCH 3 )Mn(CO) 2 ( 4chelate ), and ( η 1 : η 5 -C 5 H 4 CH 2 CH 2 COOCH 3 )Mn(CO) 2 ( 5chelate ) occurred within a few minutes, whereas 2chelate and 3chelate required refluxing for several hours to convert them to the substituted products. The substituted products have the general formula ( η 5 -C 5 H 4 R)Mn(CO) 2 L (where R is the substituent of either 1–5 and L is either a phosphine, phosphite, or tetrahydrothiophene). The weaker MnO bond was suggested for the differences in the reactivities of the chelated complexes.

Nine different substituted cyclopentadienyl ligands, which have substituents that may either chelate or bridge to second metal center, have been prepared from nucleophilic substitution reactions of esters or alkyl halides with NaCp. The sodium or thallium salts of these ligands were isolated as solids and characterized by 1 H NMR. The alkyl halide and NaCp reaction proved to yield the purer salts of the ligands because of the milder reaction conditions. These salts were reacted futher with Mn(CO) 5 Br to form the corresponding manganese tricarbonyl derivatives (i.e. (C 5 H 4 R)Mn(CO) 3 ; where R = C(O)CH 2 OCH 3 , C(O)CH 2 SCH 3 , C(O)CH 2 CH 2 SCH 3 , CH 2 CO 2 CH 3 , CH 2 CO 2 CH 2 CH 3 , CH 2 CH 2 CO 2 CH 3 , CH 2 CH 2 CO 2 CH 2 CH 3 , CH 2 CH 2 O 2 CCH 3 , and CH 2 CH 2 OCH 3 ) and Na(C 5 H 4 C(O)CH 2 OCH 3 ) was reacted with Co 2 (CO) 8 to form (C 5 H 4 C(O)CH 2 OCH 3 )Co(CO) 2 . The manganese and cobalt compounds were characterized by elemental analysis, IR, 1 H, and 13 C NMR spectra.