"Unsaturated transition metal complexes are important in many stoichiometric and catalytic bond cleavage reactions. Therefore, low-coordinate transition metal complexes coordinated with sterically hindered ancillary ligands have been used for C-H activation, N2, and CO bond cleavage reactions. In this thesis, the coordination chemistry and reactivity of low-coordinate [beta]-diketiminate cobalt and iron complexes toward bond-breaking and bond-making reactions is explored and presented. In chapter 2, the unsaturated complex LtBuCo (LtBu = bulky [beta]-diketiminate ligand) is reported. The [beta]-diketiminate ligand in LtBuCo was ligated to cobalt in a slipped [kappa]N, [eta]6-arene mode. Addition of Lewis bases to LtBuCo yielded rapid and reversible conversion to the [kappa]2N, N' mode. The rate law of ligand binding to LtBuCo was first-order in both cobalt and substrate concentration. Therefore, ligand coordination was consistent with an associative or interchange mechanism that either preceded or occurred simultaneously to [beta]-diketiminate isomerization. In addition, LtBuCo cleaved Sn-F and aryl C-F bonds, and homolytic Sn-F bond cleavage yielded [LtBuCo([mu]-F)]2. Aryl C-F bond cleavage by LtBuCo yielded [LtBuCo([mu]-F)]2 and a cobalt(II) aryl complex in a 1:2 molar ratio. [LtBuCo([mu]-F)]2 reacted with triethylsilane (Et3SiH) to give pure hydride complex [LtBuCo([mu]-H)]2, which has different properties than previously reported. In chapter 3, treatment of LMeFeNNFeLMe with 4-tert-butylpyridine (tBupy) displaced the dinitrogen ligand to give LMeFe(tBupy)2 which is formally iron(I). However, LMeFe(tBupy)2 can be defined as high-spin iron(I) with a resonance form that is high-spin iron(II) antiferromagnetically coupled to a radical on the tBupy ligand. In contrast, treatment of LMeFeNNFeLMe with pyridine (py) resulted in the reductive coupling of pyridine via C-C bond formation to give {LMeFepy}2([mu]-C10H10N2), a complex with a bridging 4,4'-bis(hydridopyridyl) ligand. {LMeFepy}2([mu]-C10H10N2) was diiron(II) in the solid state, but C-C bond formation was rapidly reversible as the solution properties were consistent with LMeFe(py)2. Chapter 4 reports new synthetic routes to iron hydride complexes with higher purity than previously achieved. The binuclear oxidative addition of H2 to a transient iron(I) intermediate yielded [LtBuFe([mu]-H)]2. This method was adapted for the synthesis of [LMeFe([mu]-H)]2, and the deuterated isotopologues, [LtBuFe([mu]-D)]2 and [LMeFe([mu]-D)]2, were synthesized using D2. The H/D exchange of hydride ligands between isotopologues and H2/D2 was observed"--Page ix-x.

This dissertation describes the synthesis, characterization, and reactivity studies of new low-coordinate complexes of readily available and inexpensive transition metals such as iron, cobalt and nickel. The compounds were magnetically characterized in detail and tested for single molecule magnet (SMM) behavior. SMMs are a topic of intense research because of their potential applications in magnetic memory, high-density information storage and quantum computing technologies. Low-coordinate compounds display magnetic moments that indicate high orbital angular momentum and are very promising candidates for SMM behavior because they also tend to have large negative zero-field splitting (D) values. The complexes reported here are stabilized by using a variety of amido, aryloxo and thiolato ligands with bulky terphenyl groups and also using aryl and alkyl substituted silylamides. A superconducting quantum interference device (SQUID) and Evans' methods were used to study the magnetic properties and single crystal X-ray crystallography and NMR (1H and 13C) were used to confirm the structures of these compounds in both the solid and solution states. Further characterization studies included UV-visible, near-IR, and IR spectroscopy, melting point, elemental analysis and DFT calculations, where applicable, in order to determine the electronic configurations and bonding schemes. At present there are ca. 100 stable open shell two-coordinate mononuclear transition metal complexes currently known but ca. 20% have a linear coordination at the metal atom with only a few being strictly 180° at their metal center. Very few of these compounds had been magnetically characterized. In Chapter 2, the synthesis and magnetic characterization of the late transition metal Co2+ (d7) and Ni2+ (d8) primary amido complexes Co{N(H)Ar(iPr6)}2, Co{N(H)Ar(Me6)}2, Ni{N(H)Ar(iPr6)}2 and Ni{N(H)Ar(Me6)}2 (Ar(Me6) = C6H3-2,6(C6H2-2,4,6-Me3)2, Ar(iPr6) = C6H3-2,6(C6H2-2,4,6-(i)Pr3)2) are described. The investigations showed that they exhibit interesting magnetic behavior. The bent versus linear geometries of the complexes enable direct observation of the effects of orbital angular momentum quenching upon bending the metal coordination geometry. The electronic configuration of the linear cobalt(II) complexes does not predict first order orbital angular momentum and yet, the magnetic moment of Co{N(H)Ar(iPr6))2 is much higher than the spin only value which suggests a large spin-orbit coupling effects due to mixing of the ground and excited states. In Chapter 3, the synthesis and characterization of the mononuclear chromium, iron, cobalt and nickel terphenyl substituted thiolate complexes Cr(SAr(Me6))2, Cr(SAr(iPr4))2, Fe(SAr(iPr4))2, Co(SAr(iPr4))2 and Ni(SAr(iPr4))2 are described. Their structures show bent coordination geometries of varying degree with strong secondary M-[eta]6 and M-C(ipso) flanking aryl ring interactions of ca. 2.153 [Angstrom] for Fe(SAr(iPr4))2, ca. 1.625 [Angstrom] for Co(SAr(iPr4))2 and ca. 1.731 [Angstrom] for Ni(SAr(iPr4))2. This observation is in sharp contrast to the almost linear coordination observed for the derivatives of the related but more crowded terphenyl thiolate ligand, SAr(iPr6), in M(SAr(iPr6))2 complexes where M = Cr, Fe, Co and Ni and the strictly linear geometry observed for the terphenyloxo analogs M(OAr(iPr4))2 where M = Fe and Co. Magnetic moments for these species are, in general, lower than the spin-only values. Expect for chromium, this is an unexpected observation for late transition metal low-coordinate complexes. The suppression of magnetic moments is most like due to the strong M-arene interactions which effectively increases the coordination number at the metal atom. These results demonstrate the important role that substituents play on the flanking rings of the terphenyl ligands and begs further investigations involving the role of dispersion in the isolation of low coordination mononuclear transition metal complexes. The divalent silylamides M{N(SiMe3)2}2 (M = Mn, Fe, and Co) are key synthons for low-coordinate transition-metal derivatives. In Chapter 4, the previously reported, but incorrectly characterized cobalt(II) silylamide, [Co{N(SiMe3)2}2]2 has been spectroscopically and magnetically characterized for the first time. In addition, the new Lewis base complexes [Co{N(SiMe3)2}2(PMe3)], and [Co{N(SiMe3)2}2(THF)], as well as a previously reported complex [Co{N(SiMe3)2}2(py)] were isolated and characterized. Magnetic studies showed that they had considerably larger magnetic moments than the spin-only value of 3.87 [mu](B), which is indicative of a significant zero-field splitting and g-tensor anisotropy. In addition to their interesting magnetic behavior and unexpectedly large D values in the range of -20 to -80 cm−1. The electronic spectrum of [Co{N(SiMe3)2}2]2 in solution showed that earlier characterization spectra of "Co{N(SiMe3)2}2" match that of the bright green THF adduct and not the dark brown cobalt dimer [Co{N(SiMe3)2}2]2. In Chapter 5, it is shown that the reaction of the versatile cobalt(II) amide, [Co{N(SiMe3)2}2]2, with four equivalents of the sterically crowded terphenyl phenols, HOAr(Me6) and HOAr(iPr4) (Ar(iPr4) = C6H3-2,6(C6H3-2,6-(i)Pr2)2) produced the first well-characterized, monomeric two-coordinate cobalt(II) bisaryloxides, Co{OAr(Me6))2 and Co(OAr(iPr4))2. Not only are these very rare examples of two-coordinate transition metal(II) aryloxides, but the magnetic moments of both the linear and the bent species were well in excess of the spin only value for cobalt(II) ion. It was demonstrated that careful manipulation of the synthetic conditions for Co(OAr(iPr4))2 could produce varying occupancies of the cobalt(II) site and that after weighting the magnetic susceptibilities of the compounds accordingly, the moments were shown to be in close agreement with each other. Chapter 6 reports the synthesis of the unstable nickel(II) bis(silylamide) complex Ni{N(SiMe3)2}2 via the reaction of NiI2 and two equivalents of NaN(SiMe3)2 in tetrahydrofuran, as well as two of its Lewis base adducts, Ni{N(SiMe3)2}2(THF) and Ni{N(SiMe3)2}2(py)2. The reaction of two equivalents of LiN(SiMe3)2 with NiCl2(DME) in tetrahydrofuran afforded the reduced homoleptic tetrameric nickel(I) amide complex, [Ni{N(SiMe3)2}]4. This unique polymetallic structure having a Ni4N4 planar array has four S = 1/2 nickel (I) ions and an antiferromagnetic exchange coupling constant of J = -102(2) cm−1. This study provides strong evidence that the formation of nickel(II) and nickel(I) amido complexes is possible without the use of sterically demanding ligand sets.

The Inorganic Syntheses series provides all users of inorganic substances with detailed and foolproof procedures for the preparation of important and timely compounds. Includes complete, up-to-date procedures involving important inorganic substances Contains subject, contributor, and formula indexes

The newest volume in the authoritative Inorganic Syntheses book series provides users of inorganic substances with detailed and foolproof procedures for the preparation of important and timely inorganic and organometallic compounds that can be used in reactions to develop new materials, drug targets, and bio-inspired chemical entities.

The Chemistry of Iron, Cobalt and Nickel deals with the chemistry of iron, cobalt, and nickel and covers topics ranging from the occurrence and distribution of all three elements to their properties, allotropy, and analytical chemistry. Compounds of iron, cobalt, and nickel in both low and high oxidation states are also discussed. This book is divided into three sections and begins with the history of iron, along with its occurrence and distribution, allotropy, and preparation and industrial production. The nuclear, physical, and chemical properties of iron, as well as the biological importance of iron compounds, are also considered. Compounds of iron are discussed, including carbonyls and nitric oxide complexes. The next two sections deal with the history, occurrence and distribution, allotropy, analytical chemistry, and preparation and industrial production of cobalt and nickel, along with their nuclear, physical, and chemical properties. Compounds of cobalt and nickel are examined, from carbonyls and nitrosyls to cyanides and organometallic compounds. This monograph will be a useful resource for inorganic chemists.

Comprehensive Coordination Chemistry II (CCC II) is the sequel to what has become a classic in the field, Comprehensive Coordination Chemistry, published in 1987. CCC II builds on the first and surveys new developments authoritatively in over 200 newly comissioned chapters, with an emphasis on current trends in biology, materials science and other areas of contemporary scientific interest.