Insights into group 4 and 5 ansa-bis(cyclopentadienyl) complexes with a single-atom bridge

Ethylene-Bridged Hexadentate Bis(amidines) and Bis(amidinates) with Variable Binding Sites

Hexadentate bis(amidines) form versatile networks of hydrogen bonds both in solid state and solution, as revealed by X-ray crystallography, IR, and NMR spectroscopy. Moreover, the corresponding bis(amidinates) produce blue and green emissions in THF solution. Tethered tetradentate bis(amidines) have emerged in coordination chemistry, enantioselective catalysis, as building blocks for polyfunctional heterocycles, and in photoluminescent materials. The next generation of flexible bis(amidine)/bis(amidinate) platforms with up to six N-donor sites has now been established.

Strategies for the Synthesis of Chiral Carbon-Bridged Group IV ansa-Metallocenes

This minireview provides a survey of the various synthetic approaches to chiral ansa-metallocenes of Ti, Zr, and Hf containing a carbon-based bridge. The individual strategies to install substitution patterns at either the cyclopentadienyl framework or the bridging unit are highlighted with focus on the progress made towards a direct preparation of single complex stereoisomers. The review further includes the discussion of potential problems such as the formation of undesired diastereomers, the threat of racemization of enantiopure material, and synthetic challenges originating from the synthesis, purification, and isolation of the target complexes. The review has been written with the goal in mind to facilitate the design and synthesis of new chiral ansa-metallocene derivatives for emerging research areas in asymmetric catalysis and organometallic chemistry.

1,1-Olefin-bridged bis-(2-indenyl) metallocenes of titanium and zirconium

Tetrasubstituted alkenes bearing geminal 2-indenyl substituents were synthesized and metallated to form a new class of ansa titanium and zirconium metallocene complexes containing a single sp²-hybridized carbon bridge.

Syntheses and structural characterizations of inorganic ansa-metallocene analogues: ansa-ferratricarbadecaboranes

New linked cyclopentadienyl-tricarbadecaboranyl and bis-tricarbadecaboranyl dianions have been used to form the first examples of ansa-metallatricarbadecaboranyl complexes. The hybrid cyclopentadienyl-tricarbadecaboranyl dianion, Li2(+)[6-C5H4-(CH2)2-nido-5,6,9-C3B7H9](2-) (1), was produced by an initial carbon-insertion reaction of a nitrile-substituted cyclopentadiene with the arachno-4,6-C2B7H12(-) anion, followed by deprotonation to the dianion with LiH. The linked-cage bis-tricarbadecaboranyl dianion, Li2(+)[6,6'-(CH2)2-nido-(5,6,9-C3B7H9)2](2-) (2), was produced by a similar carbon-insertion route involving the reaction of two equivalents of arachno-4,6-C2B7H12(-) with succinonitrile. The reaction of 1 with an equivalent of FeCl2 produced the hybrid complex, ansa-(2-(CH2)2)-(1-η(5)-C5H4-closo-1,2,3,4-C3B7H9)Fe (3), with a crystallographic determination confirming the formation of a sandwich structure where the ring and cage are linked by the ansa -CH2CH2- group with attachment to the cage at the C2 carbon. The reaction of 2 with FeCl2 produced three isomeric ansa-(CH2)2-ferrabistricarbadecaboranyl sandwich complexes, ansa-(CH2)2-(closo-C3B7H9)2Fe (4, 5 and 6). Crystallographic determinations showed that in 4, the two tricarbadecaboranyl ligands are linked by the ansa-CH2CH2- group at the C2 and C2' cage carbons, whereas in 5 and 6 they are linked at their C2 and C4' carbons, with the structures of 5 and 6 differing in the relative positions of the C4' carbons in the two cages of each complex. The structural determinations also showed that, depending upon the linking position of the ansa-tether, constraints in cage-orientation, such as observed in 4, produce unfavorable intercage steric interactions. However, the cage fragments in these complexes can readily undergo a cage-carbon migration that moves one -carbon and its tether linkage to the more favorable 4-position. This isomerization reduces the cage steric interactions and produces configurations, such as those found for 5 and 6, where the iron cage bonding is enhanced as a result of the binding effect of the tether.

Metal (Mg, Fe, Co, Zr and Ti) complexes derived from aminosilyl substituted aminopyridinato ligand: synthesis, structures and ethylene polymerization behaviors of the group 4 complexes

Lithium N-[(N,N-dimethylamino)dimethylsilyl]-2-pyridylamidate (2) was prepared from the reaction of new compound N-[(N,N-dimethylamino)dimethylsilyl]-2-pyridylamine (1) and LiBu(n). Treatment of the lithium salt (2) with an equal equivalent of MgBr(2)(THF)(2), FeCl(2) and CoCl(2) afforded the corresponding dinuclear complexes , , and , in which metal atoms possess similar trigonal bipyramidal geometries and each ligand functions as a bimetallic bridging binding aminopyridinato moiety with N-donation from the dimethylamino group. While the stoichiometric reaction of with ZrCl(4) gave the mononuclear zirconium complex (6); the seven coordinated zirconium atom adopts a distorted pentagonal bipyramid geometry and the ligand acts as monoanionic η(2)-aminopyridinato moiety with the pendant arm coordinated via N(CH(3))(2). The reaction of with one equivalent of TiCl(4)(THF)(2) produced the interesting dinuclear titanium complex (7) owing to the elimination of a (N,N-dimethylamino)dimethylsilyl group from the original ligand, and the two titanium centers present different coordination geometries. The molecular structures of the crystalline metal complexes have been confirmed by X-ray single crystal diffraction analysis. Upon activation with methylaluminoxane (MAO), both complexes and exhibited moderate catalytic activities toward ethylene polymerization and produced high molecular weight polyethylenes with broad molecular weight distributions.

Synthesis of Bulky Zirconocene Dichloride Compounds and Their Applications in Olefin Polymerization

The bulky substituted cyclopentadienyllithium derivatives, LiC5H4(CHMeR) (R = C6H5 (1), 1-naphthyl (2), 9-anthryl (3)), were synthesized from the reaction of 6-phenylfulvene, 6-(1-naphthyl)fulvene or 6-(9-anthryl)fulvene with LiMe. The ansa-bis(cyclopentadiene) ligands Me2Si(C5HMe4){C5H4(CHMeR)} (R = C6H5 (4), 1-naphthyl (5), 9-anthryl (6)), and their lithium derivatives Li2(Me2Si(C5Me4){C5H3(CHMeR)}) (R = C6H5 (7), 1-naphthyl (8), 9-anthryl (9)) have been prepared. The zirconocene complexes, [Zr(η5-C5H5){η5-C5H4- (CHMeR)}Cl2] (R = C6H5 (10), 1-naphthyl (11), 9-anthryl (12)) and [Zr{η5-C5H4(CHMeR)}2Cl2] (R = C6H5 (13), 1-naphthyl (14), 9-anthryl (15)), were synthesized by the reaction of lithium derivatives 1-3 and [Zr(η5-C5H5)Cl3] or ZrCl4, respectively. The reaction of the lithium ansa-derivatives 7-9 and zirconium tetrachloride yielded the ansa-zirconocene complexes, [Zr(Me2Si(η5-C5Me4){η5-C5H3(CHMeR)})Cl2] (R = C6H5 (16), 1-naphthyl (17), 9-anthryl (18)). The zirconocene complexes have been tested in the polymerization of ethene and propene. The polymerization of propene with the ansa-zirconocene catalysts 16-18 gave polypropylene with 70% mmmm pentads and the symmetric zirconocene catalysts 13-15 30-60% mmmm pentads.