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Title:Low-valent early transition metal complexes stabilized by the chelating tripod phosphine ligand ( t-butyl)tris((dimethylphosphino)methyl);silane ("trimpsi")
Author(s):Gardner, Thomas George
Department / Program:Chemistry
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Chemistry, Inorganic
Abstract:The organometallic chemistry of the early first-row metals has been extended through the use of a new tridentate phosphine ligand, Bu$\sp{\rm t}$Si(CH$\sb2$PMe$\sb2$)$\sb3$, or "trimpsi". The starting materials (trimpsi)TiCl$\sb3$(thf), (trimpsi)VCl$\sb3$(thf), (trimpsi)CrCl$\sb3$, and (trimpsi)ZrCl$\sb4$(dme) have been used to prepare new carbonyl, arene, and alkyl complexes of the early transition metals.
The 18-electron titanium carbonyl complex, (trimpsi)-Ti(CO)$\sb4$, is prepared by reductive carbonylation of (trimpsi)TiCl$\sb3$(thf) with sodium naphthalenide. It has a carbonyl $\sp{13}$C NMR chemical shift which is unusually far downfield, and an abnormally low IR stretching force constant, indicting unusually strong metal-to-ligand $\pi$ back-bonding. Although titanium(0) is only d$\sp4$, its relatively low effective nuclear charge places the d orbitals at unusually high energies, promoting better $\pi$ overlap with the ligand $\pi\sp\*$ orbitals. Unlike the few known low-valent titanium carbonyls, (trimpsi)-Ti(CO)$\sb4$ shows remarkable thermal and oxidative stability. Similar conclusions have been made for the related complexes (trimpsi)Zr(CO)$\sb4$ and (trimpsi)VH(CO)$\sb3$.
The 16-electron (trimpsi)Ti($\eta\sp6$-naphthalene) and the 17-electron (trimpsi)V($\eta\sp6$-naphthalene) are rare examples of early transition metal arene complexes, and are isolable intermidiates in the preparation of the trimpsi metal carbonyls. Unlike other known titanium(0) arene complexes, (trimpsi)Ti($\eta\sp6$-naphthalene) is paramagnetic. The X-ray crystal structure of (trimpsi)Ti($\eta\sp6$-naphthalene) shows a coordinated naphthalene ring that is warped at a dihedral angle of 12.4$\sp\circ$, whereas Ti(C$\sb6$H$\sb6$)$\sb2$ and Ti(C$\sb6$H$\sb5$CH$\sb3$)$\sb2$ have planar arene rings, and the naphthalene ring in (trimpsi)V-($\eta\sp6$-naphthalene) has a dihedral angle of only 5.1$\sp\circ$. Like the group 4 carbonyls, (trimpsi)Ti($\eta\sp6$-naphthalene) exhibits exceptionally strong & back-bonding from the filled Ti 3d$\sb{\rm x}\sp2\sb{\rm -y}\sp2$ orbital to the naphthalene L.U.M.O. The ring warps such that the carbon atoms with the greatest L.U.M.O. coefficient have the shortest metal-carbon distances. In general, the greater the dihedral angle, the stronger the $\delta$ back-bonding.
The 15-electron complexes (trimpsi)CrEt$\sb3$ and (trimpsi)-CrBu$\sp{\rm n}\sb3$ are thermally stable at room temperature, and undergo $\beta$-elimination only at elevated temperatures. The $n$-butyl ligands in (trimpsi)CrBu$\sp{\rm n}\sb3$ are structurally similar to those of $n$-butyl-main group compounds. These trialkylchromium(III) complexes are poor ethylene polymerization catalysts. The vanadium(III) alkyl (trimpsi)V(CH$\sb2$SiMe$\sb3$)Cl$\sb2$ has also been prepared.
The chemistry of trimpsi organoyttrium complexes has also been briefly explored.
Issue Date:1989
Rights Information:Copyright 1989 Gardner, Thomas George
Date Available in IDEALS:2011-05-07
Identifier in Online Catalog:AAI9010859
OCLC Identifier:(UMI)AAI9010859

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