Barrett E. Eichler

The synthesis and structure of sterically encumbered terphenyl tin(II) halide derivatives: simultaneous existence of monomers and dimers in the crystalline phase

Abstract The reaction of Et2O·LiC6H3-2,6–Trip2 (Trip=C6H2–2,4,6-i-Pr3) with SnCl2 afforded the two coordinate monomer Sn(Cl)C6H3-2,6–Trip2 (1), and its dimer {Sn(μ-Cl)C6H3–2,6-Trip2}2 (2), as orange and yellow crystals, respectively. Solution 119Sn NMR spectroscopy of 2 in C6D6 solution showed that it dissociated readily to give 1. The addition of pyridine (py) to a solution of 1 yielded the adduct py·Sn(Cl)C6H3–2,6-Trip2 (3) which featured tin in a three coordinate pyramidal environment. The reaction of the closely related bulky terphenyl lithium reagent LiC6H3–2,6-Dipp2 (Dipp=C6H3–2,6-i-Pr2) with SnCl2 afforded the mixed halide species {Sn(μ-Cl)0.35(μ-I)0.65C6H3–2,6-Dipp2}2 (4). This arose from the preparation of the lithium aryl precursor in situ from IC6H3–2,6-Dipp2 and n-BuLi. The monomeric nature of 1, and the weak association of 2 and 4, were attributed to the large size of the terphenyl ligands. All compounds were characterized by X-ray crystallography, 1H, 13C and 119Sn NMR spectroscopy, and IR and UV–Vis spectroscopy.

Synthesis and characterization of the monomer Ga{(NDippCMe)2CH} (Dipp = C6H3Pri2-2,6): a low valent gallium(I) carbene analogue

The reaction between solvent free Li{(NDippCMe)2CH} (Dipp = C6H3Pri2-2,6), ‘GaI’ and potassium in toluene afforded Ga{(NDippCMe)2CH} 1 which features a V-shaped, two-coordinate, six-electron gallium(I) center electronically analogous to a singlet carbene carbon.

In8(C6H3-2,6-Mes2)4 (Mes=C6H2-2,4,6-Me3): A Metal-Rich Main-Group Cluster with a Distorted Cubane Structure

A distorted In(8) cubane core (see picture) is present in the novel indium cluster In(8)(C(6)H(3)-2,6-Mes(2))(4) (Mes=C(6)H(2)-2,4,6-Me(3)), which was synthesized by the reaction of LiC(6)H(3)-2,6-Mes(2) with InCl. It has an average In-In bond length of 2.92 A and represents a new addition to the range of heavier Group 13 element clusters.

Chemistry of group 14 heteroallenes

Publisher Summary This chapter reviews allenes that have at least one carbon atom replaced by a heavier group 14 atom, commonly referred to as a heteroallene. The key issue in determining which model applies to a particular system is the singlet-triplet energy difference’ for both atoms involved in bonding. Typically, the triplet state is favored only for carbon, whereas silicon, germanium, tin, and lead favor the singlet state. The filled orbitals of the heavier atoms are progressively richer in s-character and therefore the singlet state becomes more energetically favorable down the periodic table. Trans bending of the substituents and bending at the central carbon for silaketene become dominant for its calculated structure. The Si-C-O angle is calculated to be 167.4 and the angle created between the Si-C bond and the vector bisecting the two Si-H bonds becomes a very sharp 89.0. The isolation of the 1,2,3-tristannaallene shows that any combination of heteroatoms may be combined to form allenes.

The synthesis and structure of lithium derivatives of the sterically encumbered β-diketiminate ligand [{(2,6-Pri2H3C6)N(CH3)C}2CH]−, and a modified synthesis of the aminoimine precursor

The reaction of the β-aminoimine compound (2,6-Pri2H3C6)NC(CH3)CHC(CH3)N(C6H3-2,6-Pri2)H (1, Dipp2nacnacH; Dipp = C6H3-2,6-Pri2) with n-BuLi in diethyl ether or tetrahydrofuran afforded the solvates Dipp2nacnacLi(Et2O) (2) and Dipp2nacnacLi(THF) (3), respectively, which crystallized as monomers featuring the Li+ ions in a distorted trigonal planar environment and an essentially planar arrangement for the LiN2C3 ring. The lithiation of 1, in the absence of a donor solvent, afforded a Dipp2nacnacLi product that crystallized in two different types of associated structures, 4a and 4b. In the dimer 4a, the Li+ ion is coordinated to the two nitrogens of the Dipp2nacnac ligand, and it is associated by coordination of lithium to a carbon of the Dipp ring of the other Dipp2nacnac unit of the dimer. In the dodecamer 4b, the asymmetric unit consists of a chain of six LiDipp2nacnac units associated by interactions of the Li+ ions with one or two carbons from a Dipp ring of the next molecule in the chain. The hexamer is linked to an identical one (generated through an inversion center) by Li+–Dipp interactions involving the first and third lithium atoms from each hexamer, thereby generating an overall dodecameric structure of a type that was previously unknown for lithium salts. An improved yield synthesis for 1 was also developed.

Synthesis and solid state structures of increasingly sterically crowded 1,4-diiodo-2,3,5,6-tetraarylbenzenes: a new series of bulky benzenes and aryls

A series of very bulky 1,4-diiodo-2,3,5,6-tetraarylbenzenes I2Ar4C6 (Ar = 4-tBuC6H4, 1; Ar = 3,5-tBu2C6H3, 2; Ar = 2,4,6-Me3C6H2, 3) have been prepared by a rapid, convenient procedure involving sequential reaction of hexabromobenzene with the appropriate Grignard reagent in excess, followed by addition of excess elemental iodine. The new materials 2 and 3 were isolated in 18 and 28% yields, respectively. The solid state structures of 1–3 have been investigated by single crystal X-ray techniques. Interesting distortions in the structures of these hexasubstituted benzenes are observed upon the increasing steric pressures in 1–3. For example, while the structures of 1 and 2 contain central planar benzene rings, steric interactions in 3 produce a non-planar central benzene ring. Regardless of these factors, the carbon–iodine bond lengths in 1–3 are essentially constant (2.108–2.118 A).