Synthesis And Properties Of PXP(X= C, N, P, P(O)) Pincer Iron, Cobalt And Nickel Complexes

The widespread presence of hydrocarbons makes the C-H bond activation attracting more and more attention. The value of research on C-H bond activation is embodied not only in the inert nature of C-H bonds, but also in the economic benefits in organic synthesis. In the early studies, cleavage of C-H bonds was generally realized under a severe reaction condition. With the development of research on C-H activation, cleavage of C-H bonds supported by transition metal has become one of the most important strategies and obtained more and more attention. In this field, most of the work has been realized by taking advantage of chelation on anchoring groups via cyclometalation reactions. However, the C-H activation research mainly focused on C(sp)-H and C(sp2)-H bond because of high bond energy and low polarity of C(sp3)-H bond.The special structure in pincer ligand could facilitate the activation of C-H bond by metal center through dicyclometalation reaction. Due to inertness of C(sp3)-H bond, it is relatively difficult to construct and synthesis PC(sp3)P pincer ligands. In the limited types of PC(sp3)P pincer ligands, cleavage of C(sp3)-H bond was almost realized by precious metals(Ir, Rh, Os, Ru, Pt, Pd etc.) and seldom samples involved cheap metals such as Fe and Co.In previous catalysis researches, precious metals (Ir, Rh, Os, Ru, Pt etc.) were preferred for their advantages in catalytic performance, chemo-and regio-selectivity. Nevertheless, precious metals were also restricted for the high cost, toxicity and limited availability which rendered researchers to explore economically available metals for catalysis reaction and iron was one ideal choice. In iron-catalyzed reduction reactions, it was widely accepted that hydrido iron complexes often acted as catalytic intermediates and some pincer hydrido iron complexes even possessed comparable catalytic performance with precious metals.This dissertation is mainly divided into four sections.1. Synthesis and properties of PC(sp3)P iron, cobalt and nickel pincer complexes generated by C(sp3)-H activation.Oxidative addition reaction of L1{(Ph2P-(C6H4))2CH2} with Fe(PMe3)4 generated hydrido iron complex 1 by C(sp3)-H cleavage which showed good performance in catalytic hydrosilylation of aldehydes and ketones and the catalyst loading could be reduced to 0.3 mol%.The generation of complex 2 underwent one C(sp3)-H activation process and one C(sp2)-H activation process from the reaction of L1 and FeMe2(PMe3)4. CoMe(PMe3)4, CoMe2(PMe3)3 and CoMe3(PMe3)3 could also realize the C(sp3)-H activation and generated the same product 3. Single electron oxidative addition reactions of complex 3 with alkyl halides could generate complexes 4,5 and 6.Unlike Fe(PMe3)4, Co(PMe3)4 and Ni(PMe3)4 failed to activate the C(sp3)-H bond in L1 and only generated complexes 8 and 9 after ligand substitution.2. Reaction condition optimization in synthesis and properties of POC(sp3)OP iron and cobalt pincer complexes generated by C(sp3)-H activation.Reaction condition optimization was explored for synthesis of complexes 11-13. The measurement for magnetic susceptibility of paramagnetic complex 12 was conducted.3. Synthesis and properties of PNP, PPP and PP(O)P iron, cobalt and nickel pincer complexes.Considering the excellent performance of hydrido iron complex 1 in catalytic hydrosilylation of aldehydes and ketones, we attempted to explore the difference in properties caused by changes in structures and synthesized PNP pincer ligand L5 {(Ph2P-(C6H4))2NH}.Unfortunately, reacting with Fe(PMe3)4, L5 failed to yield hydrido iron complex, only gave Fe(I) complex 14 by N-H activation. The magnetic susceptibility measurement of complex 14 was also conducted.Reactions of L5 with CoMe(PMe3)4, Co(PMe3)4 and CoCl(PMe3)3 yielded the same compound 15, the formation mechanism of which had been elucidated by in situ IR and NMR. Ni(PMe3)4 failed to activate the N-H bond in L5, only yielded simply coordinated complex 16.In the exploration of PPP pincer ligand L7{(Ph2P-(C6H4))2PH}, due to the strong electron donating effect of trivalent phosphorus, electron-rich metal complexes failed to realize P-H cleavage which could be verified by the isolation of complex 18 from the reaction of L7 with Ni(PMe3)4. To settle this problem, we synthesized PP(O)P pincer ligand L8{(Ph2P-(C6H4))2P(O)H}. L8 underwent reactions with CoMe(PMe3)4, Co(PMe3)4, CoCl(PMe3)3,Ni(PMe3)4and Fe(PMe3)4, leading to P-H bond cleavage and generating four new pincer complexes 19-22 respectively.4. Synthesis and properties of PC(sp2)P metal complexes.The reaction of PC(sp2)P pincer ligand L9 with Fe(PMe3)4 generated one unexpected three-membered metalcycle hydrido iron complex 23 which underwent the C(sp3)-H bond activation process in the benzyl position. From the reaction of L9 with 2 eq. Fe(PMe3)4, dihydrido iron complex 24 was generated. Dimetalation product 25 could be obtained through the reaction between 23 and CoMe(PMe3)4. In spite of the thermal unstability, complexes 23-25 still displayed certain activities in catalytic hydrosilylation of aldehydes.In the dissertation, we carried detailed characterizations (IR, NMR and X-Ray single diffraction etc.) for new compounds separated from different reactions.