The new iron carbonyl cyanide trans-[Fe(CN)(2)(CO)(3)](2)(-), [2](2)(-), forms in high yield via photosubstitution of Fe(CO)(5) with 2 equiv of Et(4)NCN. Protonation of [2](2)(-) generated [HFe(CN)(2)(CO)(3)](-), [2H](-), the first H-Fe-CN-CO species. Further protonation gives dihydrogen. This simple system provides insights into hydrogen evolution by the hydrogenase enzymes, which also feature H-Fe-CN-CO centers.
Tp2Ti [Tp = hydrotris(pyrazol-1-yl)borate] is a stable hard donor complex of divalent titanium that shows controlled reaction chemistry with simple chalcogen oxidants.
Ortho-linked polyphenols, quaterphenol L(OH)4, and moderately hindered terphenol PhL(OH)3 are developed as new multidentate polyaryloxide ligands for transition-metal chemistry. The polyphenols are synthesized using ortho-metalation and metal-catalyzed cross-coupling methodologies; the synthetic routes allow for facile electronic and steric modification of the basic ligand design. The Ti(IV) coordination chemistry of these ligands reveals a diverse collection of bridged structures: dimeric [Ti(mu-PhLO3)(OiPr)]2 (P2(1)/n, a = 12.2699(5) A, b = 11.7957(5) A, c = 21.238(1) A, beta = 94.551(1) degrees, Z = 2, T = 170(2) K), dimeric [Ti2(mu-PhLO3)2(mu-Cl)(Cl)(THF)] (P1, a = 11.212(1) A, b = 14.165(1) A, c = 22.447(2) A, alpha = 90.440(4) degrees, beta = 93.345(4) degrees, gamma = 111.164(4) degrees, Z = 2, T = 170(2) K), and trimeric [Ti3(mu,mu'-LO4)(mu-OiPr)2(OiPr)6] P2(1)/n, a = 11.1022(5) A, b = 18.7015(9) A, c = 24.409(1) A, beta = 95.369(2) degrees, Z = 4, T = 170(2) K). The reaction of TiCl3(THF)3 with [PhLO3]3- results in oxidation of Ti(III) to Ti(IV) and formation of the oxo dimer [Ti(PhLO3)(THF)]2(mu-O) (P1, a = 10.8649(6) A, b = 12.1882(7) A, c = 14.3349(9) A, alpha = 65.602(3) degrees, beta = 84.390(3) degrees, gamma = 86.582(3) degrees, Z = 1, T = 200(2) K); the oxo group presumably originates from the THF solvent. The titanium centers in these environments are either 5- or 6-coordinate, with distorted square pyramidal/trigonal bipyramidal and distorted octahedral geometries, respectively; the polyphenoxide chelate ligands are capable of bridging multiple oxophilic titanium sites.
The structural coordination chemistry of the sterically hindered 3,3'-bis(triphenylsilyl)-1,1'-bi-2-phenoxide ligand ([(TPS)LO(2)](2)(-)), an isosteric homologue of a chiral binaphthoxide ligand used in asymmetric induction, has been investigated on Fe(II), Fe(III), and Cr(II). The ligand diol ((TPS)L(OH)(2), 2) can be prepared on a multigram scale from 2,2'-dimethoxybiphenyl via a convenient, two-step ortho-metalation/silylation/deprotection sequence; the sodium salt of the ligand dianion (Na(2)[(TPS)LO(2)], 3) can be obtained by NaH deprotonation and was crystallographically characterized with two THF ligands bound to each cation. Protonolysis of Fe[N(SiMe(3))(2)](2) or Cr[N(SiMe(3))(2)](2)(THF)(2) with biphenol 2 in arene solvent gives [Fe(mu-(TPS)LO(2))](2) (4) or ((TPS)LO(2))Cr(THF)(2) (9), respectively, while anion metathesis of FeCl(2) or FeCl(3)/bipy with biphenoxide salt 3 in THF yields ((TPS)LO(2))Fe(THF)(2) (8) or ferric monomer ((TPS)LO(2))FeCl(bipy) (10), respectively. Dimer 4 reacts with exogenous ligands to form monomeric ligand adducts of Fe(II): with py, ((TPS)LO(2))Fe(py)(2) (5); with bipy, ((TPS)LO(2))Fe(bipy) (6); with XyNC (Xy = 2,6-xylyl), ((TPS)LO(2))Fe(CNXy)(4) (7); and with THF, 8. Complexes were characterized in solution by (1)H NMR and in the solid state by single-crystal X-ray diffraction. The 4-coordinate complexes (5, 6, 8, 9) adopt skew-distorted tetrahedral (for Fe(II)) or square planar (for Cr(II)) geometries; the 5- and 6-coordinate complexes (10 and 7) assume more typical distorted square pyramidal/trigonal bipyramidal and cis-octahedral stereochemistries. Dimer 4 possesses an unusual structure where each Fe(II) center is pseudo-4-coordinate and each biphenoxide ligand provides one terminal phenoxide donor, one bridging phenoxide, and a weak aromatic pi-interaction from one of the phenyl groups of a SiPh(3) substituent. The steric influence of the hindered biphenoxide ligand within the coordination sphere is revealed structurally through distortion of coordination polyhedra in the 4-coordinate species and through conformational and deformational changes within the biphenoxide ligand itself.
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