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The monomeric iron(II) amido derivatives are prepared and analyzed in order to determine the effects of geometric changes on their unusual magnetic properties. The data for the two amido complexes have shown a very large quenching of the orbital magnetic moment upon bending the linear geometry and also a strong correlation of high internal orbital field component ([H.sub.L]) with overall formal symmetry.

The synthesis and characterization of a range of Sn(II) hydrides are described and shown that modification of the terphenyl ligand has produced different structural types. Hydrides and relevant model species have shown that increased steric hindrance has favored the asymmetric form ArSnSn[(H).sub.2]Ar relative to the centrosymmetric isomer due to the widening of the interligand angles at tin.

The synthesis and structural characterization of the first homologous, molecular M-M bonded series for the group 12 metals are described. The results have shown that the decomposition of Ar'Cd[([mu-H).sub.2]CdAr' at room temperature has led to the M-M bonded Ar'CdCdAr', thus supporting the view that the reduction of the reduction of the iodide has proceeded via the hydride intermediate.

A simple donor-stabilization strategy is used to prepare a new class of stable main group species featuring P[double bond]B and As[double bond]B bonds. The attempts to generate the Sb[double bond]B analogue were not successful, but the formation of a stable B-N triple bond has occurred in preference to a donor-stabilized B[double bond]N double bond.

The complexes M(II){N(H)ArPr16}2 (M = Co, 1 or Ni, 2; ArPr16 = C6H3 -2,6(C6H2-2,4,6-Pr'3)2), which have rigorously linear, N-M-N = 180°, metal coordination, and M(II){N(H)ArMe6}2 (M = Co, 3 or Ni, 4; ArMe6 = C6H32,6(C6H2-2,4,6-Me3)2), which have bent, N-Co-N = 144.1(4)°, and N-Ni-N = 154.60(14)°, metal coordination, were synthesized and characterized to study the effects of the metal coordination geometries on their magnetic properties. The magnetometry studies show that the linear cobalt(II) species 1 has a very high ambient temperature moment of about 6.2 μB (cf. spin oniy value = 3.87 μB) whereas the bent cobalt species 3 had a lower μB value of about 4.7 μB. In contrast both the linear and the bent nickel complexes 2 and 4 have magnetic moments near 3.0 μB at ambient temperatures, whirls is dose to the spin only value of 2.83 μB. The studies suggest that in the linear cobalt spedes 1 there is a vely strong enhanced spin orbital coupling which leads to magnetic moments that broach the free ion value of 6.63 P8 probably as a result of the relatively weak ligand field and its rigorously linear coordination. For the linear nickel species 2, however, the expected strong first order orbital angular momentum contribution does not occur (cf. free ion value 5.6 μB) possibly bemuse of zr bonding effects involving the nitrogen p orbitals and the dxz and dyz orbitals (whose degeneracy is lifted in the C2h local symmetry of the Ni(N(H)C(q,so)}2 array) whirls quench the orbital angular momentum. [ABSTRACT FROM AUTHOR]

The synthesis and characterization of the mononuclear chromium(II) terphenyl substituted primary amido-complexes Cr{N(H)ArPri6}2 (ArPri6 = C6H3-2,6-(C6H2-2,4,6-iPr3)2 (1), Cr{N(H)ArPri4}2 (ArPri4 = C6H3-2,6-(C6H3-2,6-iPr2)2 (2), Cr{N(H)ArMe6}2 (ArMe6 = C6H3-2,6-(C6H2-2,4,6-Me3)2 (4), and the Lewis base adduct Cr{N(H)ArMe6}2(THF) (3) are described. Reaction of the terphenyl primary amido lithium derivatives Li{N(H)ArPri6} and Li{N(H)ArPri4} with CrCl2(THF)2 in a 2:1 ratio afforded complexes 1 and 2, which are extremely rare examples of two coordinate chromium and the first stable chromium amides to have linear coordinated high-spin Cr2+. The reaction of the less crowded terphenyl primary amido lithium salt Li{N(H)ArMe6} with CrCl2(THF)2 gave the tetrahydrofuran (THF) complex 3, which has a distorted T-shaped metal coordination. Desolvation of 3 at about 70 °C gave 4 which has a formally two-coordinate chromous ion with a very strongly bent core geometry (N-Cr-N= 121.49(13)°) with secondary Cr--C(aryl ring) interactions of 2.338(4) Å to the ligand. Magnetometry studies showed that the two linear chromium species 1 and 2 have ambient temperature magnetic moments of about 4.20 μB and 4.33 μB which are lower than the spin-only value of 4.90 μB typically observed for six coordinate Cr2+. The bent complex 4 has a similar room temperature magnetic moment of about 4.36 μB. These studies suggest that the two-coordinate chromium complexes have significant spin-orbit coupling effects which lead to moments lower than the spin only value of 4.90 μB because λ (the spin orbit coupling parameter) is positive. The three-coordinated complex 3 had a magnetic moment of 3.79 μB. [ABSTRACT FROM AUTHOR]

Reaction of M(N(SiMe3)2)2 (M = Ge, Sn, or Pb) with the sterically encumbered primary phosphine Ar'PH2 (2), Ar1 = C6H3-2.6-(C6H3-2,6-Pr'2), at ca. 200 °C afforded the highly colored phosphinidene dimers (M(μ-PAr'))2, M = Ge(3), Sn(4), or Pb(5), with disilylamine elimination. The compounds were characterized by single-crystal X-ray crystallography and heteronuclear NMR spectroscopy. The structures of 3.4, and 5 featured similar M2P2 ring cores, of which 4 and 5 have 50/50 P atom disorder, consistent with either a planar four-membered M2P2 arrangement with anti aryl groups or with an M2P2 ring folded along the M-M axis with syn aryl groups. A syn-folded structure was resolved for the Ge2P2 ring in compound 3. The M-P distances resembled those in M( II) phosphido complexes and are consistent with single bonding. The coordination geometries at the phosphorus atoms are pyramidal. DFT calculations on the gas phase models (M(μ-PMe))2 (M = Ge, Sn. Pb) agreed with the syn (M-M folded) structural interpretation of the X-ray data. The synthesis of the bulky phosphine Ar'PH2 2 with the use of the aryl transfer agent Ar'MgBr(THF)2 is also reported. This route afforded a significantly higher yield of product than that which was obtained using LiAr', which tends to result in aryl halide elimination and the observation of insoluble red phosphorus. [ABSTRACT FROM AUTHOR]

Reaction of the hindered phosphino- and arsinoboranes, Ar*Pn(H)-B(Br)Tmp (Ar* = -C6H3-2,6-(C6H2-2,4,6-iPr3)2 Tmp = 2,2,6,6-tetramethylpiperidino; Pn = P and As, 1 and 3, respectively) with 4-dimethylaminopyridine, DMAP, afforded the boranylidenephosphane and arsane, Ar*PnB(DMAP)Tmp (Pn = P and As, 2 and 4) as deep red- purple solids. The analogous aminoboranes Ar′N(H)-B(X)Tmp (Ar′ = -C6H3-2,6-(C6H2-2,4,6-Me3)2; X = Cl and Br; 5 and 6) did not display any reactivity with DMAP, but in the presence of the amide base, Na[N(SiMe3)2], the clean formation of the uncomplexed iminoborane Ar′NBTmp (7) was observed. Attempts to generate an SbB bond were unsuccessful, as the required stibinoborane precursor, Ar*Sb(H)-B(Br)Tmp, could not be prepared; in place of clean Sb-B bond formation, the reduced product Ar*SbSbAr* was obtained. All compounds were characterized spectroscopically, and the X-ray crystal structures of 1, 2, 4, 6, and 7 were determined. [ABSTRACT FROM AUTHOR]

A series of symmetric divalent Sn(ll) hydrides of the general form [(4-X-Ar′)Sn(μ-H)]2 (4-X-Ar′ = C6H2-4-X-2,6-(C6H3-2,6-iPr2)2; X = H, MeO, tBu, and SiMe3; 2, 6, 10, and 14), along with the more hindered asymmetric tin hydride (3,5-iPr2-Ar*)SnSn(H)2(3,5-iPr2-Ar*) (16) (3,5-iPr2-Ar* = 3,5-iPr2-C6H-2,6-(C6H2-2,4,6-iPr3)2), have been isolated and characterized. They were prepared either by direct reduction of the corresponding aryltin(ll) chloride precursors, ArSnCI, with LiBH4 or tBu2AIH (DIBAL), or via a transmetallation reaction between an aryltin(ll) amide, ArSnNMe2, and BH3·THF. Compounds 2, 6, 10, and 14 were obtained as orange solids and have centrosymmetric dimeric structures in the solid state with long Sn···Sn separations of 3.05 to 3.13 Å. The more hindered tin(ll) hydride 16 crystallized as a deep-blue solid with an unusual, formally mixed-valent structure wherein a long Sn-Sn bond is present [Sn-Sn = 2.9157(10) Å] and two hydrogen atoms are bound to one of the tin atoms. The Sn-H hydrogen atoms in 16 could not be located by X-ray crystallography, but complementary Mössbauer studies established the presence of divalent and tetravalent tin centers in 16. Spectroscopic studies (IR, UV-vis, and NMR) show that, in solution, compounds 2, 6, 10, and 14 are predominantly dimeric with Sn-H-Sn bridges. In contrast, the more hindered hydrides 16 and previously reported (Ar*SnH)2 (17) (Ar* = C6H3-2,6-(C6H2-2,4,6-iPr3)2) adopt primarily the unsymmetric structure ArSnSn(H)2Ar in solution. Detailed theoretical calculations have been performed which include calculated UV-vis and IR spectra of various possible isomers of the reported hydrides and relevant model species. These showed that increased steric hindrance favors the asymmetric form ArSnSn(H)2Ar relative to the centrosymmetric isomer [ArSn(μ-H)]2 as a result of the widening of the interligand angles at tin, which lowers steric repulsion between the terphenyl ligands. [ABSTRACT FROM AUTHOR]

The synthesis and structural characterization of the first homologous, molecular M-M bonded series for the group 12 metals are reported. The compounds Ar′MMAr′ (M = Zn, Cd, or Hg; Ar′ = C6H3-2,6-(C6H3-2,6-Pr′2)2) were synthesized by reduction of the corresponding arylmetal halides by alkali metal! graphite (Zn or Hg) or sodium hydride (Cd). These compounds possess almost linear C-M-M-C core structures with two-coordinate metals. The observed M-M bonds distances were 2.3591(9), 2.6257(5), and 2.5738(3) Å for the zinc, cadmium, and mercury species, respectively. The shorter Hg-Hg bond in comparison to that of Cd-Cd is consistent with DFT calculations which show that the strength of the Hg- Hg bond is greater. The arylmetal halides precursors (Ar′Ml)1 or 2, and the highly reactive hydrides (Ar′MH)1 or 2, were also synthesized and fully characterized by X-ray crystallography (Zn and Cd) and multinuclear NMR spectroscopy. The arylzinc and arylcadmium iodides have iodide-bridged dimeric structures, whereas the arylmercury iodide, Ar′Hgl, is monomeric. The aryizinc and arylcadmium hydrides have symmetric (Zn) or unsymmetric (Cd) p-H-bridged structures. The Ar′HgH species was synthesized and characterized by spectroscopy, but a satisfactory refinement of the structure was precluded by the contamination of monomeric Ar′HgH by Ar′H. It was also shown that the decomposition of Ar′Cd(μ-H)2CdAr′ at room temperature leads to the M-M bonded Ar′CdCdAr′, thereby supporting the view that the reduction of the iodide proceeds via the hydride intermediate. [ABSTRACT FROM AUTHOR]

The complexes M(II){N(H)Ar(Pr(i)(6))}(2) (M = Co, 1 or Ni, 2; Ar(Pr(i)(6)) = C(6)H(3)-2,6(C(6)H(2)-2,4,6-Pr(i)(3))(2)), which have rigorously linear, N-M-N = 180°, metal coordination, and M(II){N(H)Ar(Me(6))}(2) (M = Co, 3 or Ni, 4; Ar(Me(6)) = C(6)H(3)-2,6(C(6)H(2)-2,4,6-Me(3))(2)), which have bent, N-Co-N = 144.1(4)°, and N-Ni-N = 154.60(14)°, metal coordination, were synthesized and characterized to study the effects of the metal coordination geometries on their magnetic properties. The magnetometry studies show that the linear cobalt(II) species 1 has a very high ambient temperature moment of about 6.2 μ(B) (cf. spin only value = 3.87 μ(B)) whereas the bent cobalt species 3 had a lower μ(B) value of about 4.7 μ(B). In contrast, both the linear and the bent nickel complexes 2 and 4 have magnetic moments near 3.0 μ(B) at ambient temperatures, which is close to the spin only value of 2.83 μ(B). The studies suggest that in the linear cobalt species 1 there is a very strong enhanced spin orbital coupling which leads to magnetic moments that broach the free ion value of 6.63 μ(B) probably as a result of the relatively weak ligand field and its rigorously linear coordination. For the linear nickel species 2, however, the expected strong first order orbital angular momentum contribution does not occur (cf. free ion value 5.6 μ(B)) possibly because of π bonding effects involving the nitrogen p orbitals and the d(xz) and d(yz) orbitals (whose degeneracy is lifted in the C(2h) local symmetry of the Ni{N(H)C(ipso)}(2) array) which quench the orbital angular momentum., (© 2012 American Chemical Society)

The monomeric iron(II) amido derivatives Fe{N(H)Ar*}(2) (1), Ar* = C(6)H(3)-2,6-(C(6)H(2)-2,4,6-Pr(i)(3))(2), and Fe{N(H)Ar(#)}(2) (2), Ar(#) = C(6)H(3)-2,6-(C(6)H(2)-2,4,6-Me(3))(2), were synthesized and studied in order to determine the effects of geometric changes on their unusual magnetic properties. The compounds, which are the first stable homoleptic primary amides of iron(II), were obtained by the transamination of Fe{N(SiMe(3))(2)}(2), with HN(SiMe(3))(2) elimination, by the primary amines H(2)NAr* or H(2)NAr(#). X-ray crystallography showed that they have either strictly linear (1) or bent (2, N-Fe-N = 140.9(2) degrees ) iron coordination. Variable temperature magnetization and applied magnetic field Mossbauer spectroscopy studies revealed a very large dependence of the magnetic properties on the metal coordination geometry. At ambient temperature, the linear 1 displayed an effective magnetic moment in the range 7.0-7.50 mu(B), consistent with essentially free ion magnetism. There is a very high internal orbital field component, H(L) approximately 170 T which is only exceeded by a H(L) approximately 203 T of Fe{C(SiMe(3))(3)}(2). In contrast, the strongly bent 2 displayed a significantly lower mu(eff) value in the range 5.25-5.80 mu(B) at ambient temperature and a much lower orbital field H(L) value of 116 T. The data for the two amido complexes demonstrate a very large quenching of the orbital magnetic moment upon bending the linear geometry. In addition, a strong correlation of H(L) with overall formal symmetry is confirmed. ESR spectroscopy supports the existence of large orbital magnetic moments in 1 and 2, and DFT calculations provide good agreement with the physical data.

The synthesis and structural characterization of the first homologous, molecular M-M bonded series for the group 12 metals are reported. The compounds Ar'MMAr' (M = Zn, Cd, or Hg; Ar' = C(6)H(3)-2,6-(C(6)H(3)-2,6-Pr(i)(2))(2)) were synthesized by reduction of the corresponding arylmetal halides by alkali metal/graphite (Zn or Hg) or sodium hydride (Cd). These compounds possess almost linear C-M-M-C core structures with two-coordinate metals. The observed M-M bonds distances were 2.3591(9), 2.6257(5), and 2.5738(3) A for the zinc, cadmium, and mercury species, respectively. The shorter Hg-Hg bond in comparison to that of Cd-Cd is consistent with DFT calculations which show that the strength of the Hg-Hg bond is greater. The arylmetal halides precursors (Ar'MI)(1 or 2), and the highly reactive hydrides (Ar'MH)(1 or 2), were also synthesized and fully characterized by X-ray crystallography (Zn and Cd) and multinuclear NMR spectroscopy. The arylzinc and arylcadmium iodides have iodide-bridged dimeric structures, whereas the arylmercury iodide, Ar'HgI, is monomeric. The arylzinc and arylcadmium hydrides have symmetric (Zn) or unsymmetric (Cd) mu-H-bridged structures. The Ar'HgH species was synthesized and characterized by spectroscopy, but a satisfactory refinement of the structure was precluded by the contamination of monomeric Ar'HgH by Ar'H. It was also shown that the decomposition of Ar'Cd(mu-H)(2)CdAr' at room temperature leads to the M-M bonded Ar'CdCdAr', thereby supporting the view that the reduction of the iodide proceeds via the hydride intermediate.