A. Nagl

1,1′-Bis(diphenylphosphino)ferrocene ligand substitution in the benzylidyne-capped cluster PhCCo3(CO)9. Synthesis, X-ray structure, and redox reactivity of PhCCo3(CO)7(dppf)

Abstract The reaction between 1,1′-bis(diphenylphosphino)ferrocene (dppf) and the tricobalt cluster PhCCo 3 (CO) 9 ( 1 ) yields the disubstituted cluster PhCCo 3 (CO) 7 (dppf) ( 2 ). The dppf ligand in 2 bridges adjacent cobalt centers via axial coordination. Ligand substitution leading to 2 may be achieved by thermolysis, oxidative decarbonylation using trimethylamine oxide, and by electrontransfer chain (ETC) catalysis using sodium benzophenone ketyl. The isolated yield of 2 ranged from 50 to 70% in all cases. Solution characterization of 2 by FT-IR and 31 P NMR spectroscopy is presented along with the single-crystal X-ray diffraction results. The dppf-bridged cluster PhCCo 3 (CO) 7 (dppf)·(toluene) crystallized in the monoclinic space group P 2 1 / c with a = 13.560(3), b = 17.339(3), c = 21.482(3) A, β = 106.81(1)°, V = 4835(1) A 3 and Z = 4. Block-cascade least-squares refinement yielded R = 0.0630 for 5055 ( I > 3σ( I )) reflections. The redox reactivity of 2 was examined by cyclic voltammetry, which revealed the presence of two irreversible oxidations that are attributed to the oxidation of the dppf ligand and the cluster core along with the observation of an irreversible reduction that exhibits cyclic voltammetric curve crossing. All of the redox processes are discussed with respect to existing tricobalt cluster redox chemistry.

Reaction of bis(dimethylphosphino)ethane with the tetracobalt cluster Co4(CO)10(μ4-PPh)2; synthesis, structure, and solution dynamics of Co4(CO)8(μ4-PPh)2(dmpe)

Abstract The reaction of the tetracobalt cluster Co4(CO)10(μ4-PPh)2 (1) with the bidentate ligand 1,2-bis(dimethylphosphino)ethane (dmpe) gives the disubstituted cluster Co4(CO)8(μ4-PPh)2(dmpe) (3) in high yield. The dmpe ligand is bound to a single cobalt atom in a chelating fashion as determined by FTIR and NMR (31P and 13C) spectroscopy and singlecrystal X-ray crystallography. Co4(CO)8(μ4-PPh)2(dmpe) · 1 2 toluene crystallizes in the triclinic space group P 1 with a 11.673(1), b 15.986(5), c 20.276(7) A, α 94.40(3), β 106.28(2), γ 94.89(2)°, V 3599(2) A3 and Z  4. Blockcascade least squares refinement yielded R  0.0521 for 6830 reflections. The temperaturedependent 13C NMR spectra of 3 reveal two distinct fluxional processes which serve to equilibrate the carbonyl ligands about the cluster polyhedron. The stability of 3 under different conditions has been examined by Cylindrical Internal Reflectance (CIR) spectroscopy. In benzene solution 3 is stable under 250 psi of H2 at 150°C; partial decomposition to Co(CO)−4 is observed using CO and H2/CO under analogous conditions.

Amino acid complexes of [Co(III) (trien)]+3

Seven β2 complexes have been investigated and the structural parameters compared with literature values and molecular mechanics calculations. All β2 compounds exhibit the (S,S,λλδ) or, (R,R,δδλ) configuration. Three of the β2 complexes have monocoordinated amino acids or amino acid esters while the amino acid is chelated in the others. The Co−N bondtrans to the amino acid oxygen or a Cl− varies significantly in length due to thetrans-effect. The chelate rings are twisted to minimize torsional interactions and the changes in conformation in the various structures can be modeled by molecular mechanics. In one complex the carbonyl groups of enantiomeric complexes are bridged by silver ions. In β2[Co(trien)(C-formylglycine)]Cl2 · H2O the carbonyl oxygen of the chelated amino acid is protonated and the formyl group exists in the enol form.

Synthesis, redox chemistry, and X-ray structure of the mixed-metal cluster Fe2(CO)6(μ3-S)2Ni(dppf)

The reaction between the dianion [Fe2(CO)6(μ2-S)2]2− and NiCl2(dppf) occurs readily at room temperature to give the mixed-metal cluster Fe2(CO)6(μ3-S)2Ni(dppf) in moderate yield. Fe2(CO)6(μ3-S)2Ni(dppf) was isolated by preparative chromatography and its solid-state structure established by X-ray diffraction analysis. Fe2(CO)6(μ3-S)2Ni(dppf) crystallizes in the monoclinic space group C2/c, a = 20.320(6), b = 13.114(2), c = 15.622(2) Å, β = 110.25(2)°, V = 3905.4(11) Å3, Z = 4, and dcalc = 1.630 g/cm.3 The X-ray structure of Fe2(CO)6(μ3-S)2Ni(dppf) exhibits an Fe2S2Ni arachno polyhedral core, with the pendant dppf ligand attached to an essentially square planar Ni center. The redox chemistry of Fe2(CO)6(μ3-S)2Ni(dppf) was investigated by cyclic voltammetry which showed a reversible, one-electron oxidation localized on the Fe2S2 core along with an irreversible, one-electron reduction that is antibonding with respect to the Fe—Fe and Fe—S bonds. The electrochemical assignments were confirmed by carrying out extended Hückel MO calculations on the model cluster Fe2(CO)6(μ3-S)2Ni(H4-dppf).

Reaction of Ph2PH with the tetracobalt cluster Co4(CO)10(μ4-PPh)2. Kinetic studies of sequential CO replacement and X-ray crystal structure of Co4(CO)8(μ4-PPh)2(Ph2PH)2

Abstract The kinetics for the sequential substitution of CO on the tetracobalt cluster Co 4 (CO) 10 (μ 4 -PPh) 2 have been investigated for the ligand Ph 2 PH. Ligand substitution is observed under mild conditions to yield Co 4 (CO) 10− n (μ 4 -PPh) 2 (Ph 2 PH) n ( n = 1, 2). The kinetics for each substitution step reveal a two-term rate law: ( k 1 + k 2 [Ph 2 PH])[cluster]. The k 2 component corresponds to a Ph 2 PH-dependent attack on Co 4 (CO) 10 (μ 4 -PPh) 2 and Co 4 (CO) 9 (μ 4 -PPh) 2 (Ph 2 PH). The k 1 contribution is inconsistent with a dissociative loss of CO, but rather a unimolecular closo → nido cluster rearrangement. The bis-substituted cluster Co 4 (CO) 8 (μ 4 -PPh) 2 (Ph 2 PH) 2 is observed to crystallize in the triclinic space group P 1 with a 9.800(1) A, b 14.849(2) A, c 15.583(2) A, α 83.89(1)°, β 81.69(1)°, γ 79.34(1)°, V 2197.7(5) a 3 and Z = 2. Block-cascade least-squares refinement yielded R = 0.0379 for 4860 reflections. The importances of thermodynamic product control in directing the phosphine regiochemistry and stereochemistry in Co 4 (CO) 8 (μ 4 -PPh) 2 (Ph 2 PH) 2 and other reported clusters of this genre is discussed.

A novel conformational energy preference in 7-chloro-7-carboxamido-6b,7,8,8a-tetrahydrocyclobut[A]acenaphthylene

Abstract The title compound ( E - 1 ) exhibits a conformational energy preference in which the carbonyl oxygen lies over the aromatic ring. This preferred conformation is shown to exist in the solid state by X-ray analysis of the crystal structure and in the solution phase by COSY studies of the NMR spectrum. Related compounds show no conformational preference in solution at room temperature on the NMR time scale.The computational program MMX reproduces closely the geometry of the favored conformation of E - 1 and verifies that it has a unique conformational energy minimum compared to other derivatives of this system.

X-ray diffraction structure of the phosphido-bridged mixed-metal cluster Fe2(CO)6(μ3-PPh)2Pt(dppe)

Treatment of Fe2(CO)6(μ2-PPhH)2 with BuLi (2 equiv.), followed by the addition of PtCl2 (dppe), affords the phosphido-bridged cluster Fe2(CO)6(μ3-PPh)2Pt(dppe). The Fe2Pt cluster was isolated and characterized in solution by IR and 31P NMR spectroscopy, and the molecular structure of Fe2(CO)6(μ3-PPh)2Pt(dppe) determined by X-ray diffraction analysis. Fe2(CO)6(μ3-PPh)2Pt(dppe) crystallizes in the orthorhombic space group Pbca, a = 17.539(3) Å, b = 21.490(2) Å, c = 22.959(3) Å, V = 8653.5(18) Å3, Z = 8, dcalc = 1.670 g cm−3; R = 0.0644, Rw = 0.0389 for 5040 observed reflections with I > 3σ(I).

PhPMe2 ligand substitution in the tetracobalt cluster Co4(CO)10(μ4-PPh)2 : X-ray diffraction structure of Co4(CO)8(PPhMe2)2(μ4-PPh)2

The thermal substitution chemistry of the tetracobalt cluster Co4(CO)10(μ4-PPh)2 with the phosphine ligand PhPMe2 (2.5 equiv) has been explored and found to afford the bis(phosphine)-substituted cluster Co4(CO)8(PPhMe2)2(μ4-PPh)2 as the major reaction product. The regiochemistry and stereoselectivity exhibited by the two phosphine ligands in Co4(CO)8(PPhMe2)2(μ4-PPh)2 have been unambiguously established by X-diffraction analysis as having a 1,3-cis orientation. Co4(CO)8(PPhMe2)2(μ4-PPh)2 crystallizes in the monoclinic space group P21/n,a=10.314(1) Å,b=18.051(3) Å,c=21.313(2) Å, β=90.10(1)°,V=3968.0(8) Å3,Z=4,dcalc=1.590 g cm−3;R=0.051,Rw=0.042 for 4987 observed reflections withI>3σ(I). Generalizations concerning the stereochemical disposition of two P-ligands about the Co4(CO)8P2(μ4-PPh)2 (where P=phosphine or phosphite) polyhedron are discussed with respect to the cone angle of the P-ligand and its steric interactions with the capping phenylphosphinidene group.