title: Monomeric, dimeric, and trimeric calcium compounds containing substituted pyrrolyl and ketiminate ligands: synthesis and structural characterization.
abstract: A series of monomeric, dimeric, and trimeric calcium compounds containing substituted pyrrolyl or ketiminate ligands were synthesized, and characterized by NMR spectroscopy and single crystal X-ray diffractometry. The reaction of Ca[N(SiMe(3))(2)](2)(THF)(2) with 1 equiv of [C(4)H(3)NH(2-CH(2)NEt(2))] in toluene generates the dimeric complex, [Ca{N(SiMe(3))}[mu-eta(1):eta(5)-{C(4)H(3)N(2-CH(2)NEt(2))}]](2) (1) in which two substituted pyrrolyl ligands bind two Ca centers in a eta(1) and eta(5) fashion. The reaction between Ca[N(SiMe(3))(2)](2)(THF)(2) and 2 equiv of [C(4)H(3)NH(2-CH(2)NEt(2))] in THF yields a monomeric calcium compound Ca[C(4)H(3)N(2-CH(2)NEt(2))](2)(THF)(2) (2) that exhibits a facial octahedral geometry on the central Ca atom. Similarly, the reactions of Ca[N(SiMe(3))(2)](2)(THF)(2) with 1 and 2 equiv of OCMeCHCMeNHAr (Ar = 2,6-diisopropylphenyl) generate [Ca(OCMeCHCMeNAr){N(SiMe(3))(2)}](2) (3) and [Ca(mu-OCMeCHCMeNAr)(OCMeCHCMeNAr)](2) (4), respectively. In 3, the Ca atom possesses a distorted tetrahedral geometry where as in 4, a square plane is developed by the two calcium atoms with the bridging participation of two oxygen atoms from two ketiminate ligands. The in situ reaction of OCMeCHCMeNHAr, Ca[N(SiMe(3))(2)](2)(THF)(2), and isopropyl alcohol results in a trimeric calcium alkoxide compound Ca(3)(mu-OCMeCHCMeNAr)(2)(OCMeCHCMeNAr)(mu(3)-O-(i)Pr)(2)(mu(2)-O-(i)Pr) (5). Compounds 1, 2, and 5 showed good catalytic activity in the ring-opening polymerization of epsilon-caprolactone and l-lactide.
authors.affiliation: Department of Chemistry, National Changhua University of Education, Changhua, Taiwan 50058.
authors.forename: Shih-Mao
authors.initials: SM
authors.lastname: Ho
authors.forename: Ching-Sheng
authors.initials: CS
authors.lastname: Hsiao
authors.forename: Amitabha
authors.initials: A
authors.lastname: Datta
authors.forename: Chen-Hsiung
authors.initials: CH
authors.lastname: Hung
authors.forename: Ling-Chueh
authors.initials: LC
authors.lastname: Chang
authors.forename: Ting-Yu
authors.initials: TY
authors.lastname: Lee
authors.forename: Jui-Hsien
authors.initials: JH
authors.lastname: Huang