Synthesis And Reactivity Of Calcium And Rare-Earth Complexes

In this dissertation, calcium and rare-earth complexes supported by SiMe2-bridged pyrrolyl-cyclopentadienyl ligand, tridentate imino-amidinate ligand and N-heterocyclic carbenes have been synthesized and characterized. The reactivity and catalytic reactions of these complexes have been investigated. Furthermore, a new synthetic route to2,1-benzazaboroles and2,1-benzazaborolyl anions has been developed, and the reactivity of these compounds have been explored. The details are as follows:1. Two pyrrolyl-cyclopentadienyl ligands [(C5Me4H)-SiMe2-(NC4H4)](L1H) and [(C5Me4H)-SiMe2-(C4H3NMe)](L2H) have been synthesized and characterized. The reactions of the ligands with Ca[N(SiMe3)2]2(THF)2gave heteroleptic calcium amides L1Ca{N(SiMe3)2}(2) and L2Ca{N(SiMe3)2}(8). However, compound2and8are not stable in solution, which readily undergo ligand-exchange to form homoleptic complexes.2. Bulky tridentate imino-amidinate ligand [2-{NHC(Ph)NAr}C6H4CHNAr](L3H, Ar=2,6-iPr2C6H3) was synthesized and characterized. The calcium and ytterbium complexes [L3M{N(SiMe3)2}(THF)](13, M=Ca;14, M=Yb) supported by this ligand were prepared by the reaction of L3H and M[N(SiMe3)2]2(THF)2.13and14show high thermal stability and catalyze intermolecular hydrophosphination of alkenes,1,3-dienes and alkynes with high activity and selectivity under mild conditions. High selective1,4-additions (94-100%) for the conjugated dienes examined were observed with both catalysts. The calcium complex exclusively catalyzes anti-addition to alkynes including terminal alkynes, while the ytterbium complex catalyzes syn-addition in most cases.3. A series of calcium and ytterbium NHC adducts I’PrCa[N(SiMe3)2]2(17), IMesCa[N(SiMe3)2]2(18),(IMe4)2Ca[N(SiMe3)2]2(19),(IMe4)2Yb[N(SiMe3)2]2(21) and (IMe4)(I’Pr)Yb[N(SiMe3)2]2(22) have been prepared by the reaction of [C(NRCR’)2](I’Pr, R=iPr, R’-Me; IMes, R=2,4,6-Me3C6H2, R’=H; IMe4, R=R’=Me) and M[N(SiMe3)2]2(THF)2(M-Ca, Yb). The reactivity studies showed that Ca-NHC adducts are less stable than Yb-NHC adducts. The Yb-NHC adduct21reacted readily with2equivalents of Ph2PH to form NHC-supported ytterbium diphosphide (IMe4)3Yb(PPh2)2(24). In addition,21catalyzes intermolecular hydrophosphination of alkenes and alkynes with high activity under mild conditions. Most importantly, the homogeneous catalyst can be recovered after the catalytic reaction.4. Reduction of imine-chelated boron bromides [o-C6H4(CH=NR)B(Ph)Br](26, R=2,6-iPr2C6H3;27, R=tBu) with2equivalents of alkali metal offered a new pathway to2,1-benzazaborolyl anions [o-C6H4{B(Ph)N(R)CH}]-[M]+(THF)n (33-36, R=2,6-iPr2C6H3,tBu; M=Li, K; n=1-4), which reacted readily with electrophiles to afford1,2,3-trisubstituted2,1-benzazaboroles37-41. Moreover, reduction of the boron bromides with1equivalent of alkali metal resulted in the dimerization of benzazaboroles with the formation of [o-C6H4{B(Ph)N(R)CH}]2(42, R=2,6-iPr2C6H3;43, R=tBu), as the mixture of two diastereoisomers. Interestingly, the mesomeric2,1-benzazaboroles could undergo irreversible diastereomeric isomerization to form the racemic isomer catalyzed by suitable bases. In addition, with the catalysis of nitrogen-containing bases, compound43could activate the sp3C-H bond in toluene to afford compound [o-C6H4{B(Ph)N(/Bu)CH(CH2Ph)}](44) and [o-C6H4{B(Ph)N(tBu)CH2}](45). The mechanism studies suggest that the heterolytic cleavage of a C-C bond is operative in these processes.