Biomedical subjects
Alan J. Welch
Publications and source records attributed to Alan J. Welch.
Synthesis, Molecular Structure, and Reactivity of the Tetranuclear Complex [NBu(4)](2)[Pd(4)(&mgr;-PPh(2))(2)(&mgr;-Cl)(4)(C(6)F(5))(4)]. Molecular Structure of [Pd(2)(&mgr;-PPh(2))(C(6)F(5))(2)(bipy)(2)]ClO(4).C(6)H(14).
Anionic tetranuclear complexes with the molecular formula [NBu(4)](2)[Pd(4)(&mgr;-PPh(2))(2)(&mgr;-X)(4)(C(6)F(5))(4)] [X = Cl (1), Br (2)] were obtained by reaction of [NBu(4)](2)[Pd(2)(&mgr;-PPh(2))(2)(C(6)F(5))(4)] and PdCl(2) (or K(2)[PdCl(4)]) in acetone, followed by reaction with KBr for 2. The reactions of 1 with neutral monodentate (L) or bidentate (L-L) ligands afford the dinuclear derivatives [Pd(2)(&mgr;-PPh(2))(&mgr;-Cl)(C(6)F(5))(2)L(2)] [L = PPh(3) (3), py (4)] or [Pd(2)(&mgr;-PPh(2))(C(6)F(5))(2)(L-L)(2)](n)() [n = 1-, L-L = acac (6); n = 1+, L-L = bipy (7) or phen (8)]. The structures of complexes 1 and 7 were determined by single-crystal X-ray diffraction studies. The bis(acetone) solvate of complex 1, [NBu(4)](2)[Pd(4)(&mgr;-PPh(2))(2)(&mgr;-Cl)(4)(C(6)F(5))(4)].2C(3)H(6)O, crystallizes in the monoclinic system, space group P2(1)/c, with a = 11.679(5) Å, b = 16.552(7) Å, c = 23.868(8) Å, beta = 101.10(3) degrees, V = 4527.6(15) Å(3), and Z = 2. The central core of the anion has the shape of a rectangle with the four Pd atoms in the corners. The hexane solvate of complex 7, [Pd(2)(&mgr;-PPh(2))(C(6)F(5))(2)(bipy)(2)][ClO(4)].C(6)H(14), crystallizes in the monoclinic system, space group P2(1)/n, with a = 16.214(3) Å, b = 10.311(2) Å, c = 28.380(6) Å, beta = 100.82(3) degrees, V = 4660(2) Å(3), and Z = 4. In both complexes, the long Pd.Pd distances (>3.1 Å) clearly point to the absence of any Pd-Pd interaction.
First Example of a Bis(dicarbollide) Metallacarborane Containing a B,C'-Heteronuclear Bridge.
The first example of B,C'-bridging in the commo bis(dicarbollide) series are presented. The sandwich metallacarborane synthesized is neutral due to the formation of a sulfonium group bridging one carbon from one half and one boron from the second half to yield [1',8-&mgr;-SEt-3,3'-Co(1-Ph-2-SEt-1,2-C(2)B(9)H(9))(9'-Ph-1',9'-C(2)B(9)H(8))]. A nucleophilic substitution is involved to account for its formation. A rearrangement from 3,1,2-CoC(2)B(9) to 3,1,9-CoC(2)B(9) has taken place. The molecular structure is proven by an X-ray analysis.
1-Phenyl-1,2-dicarba-closo-dodecaborane, 1-Ph-1,2-closo-C(2)B(10)H(11). Synthesis, Characterization, and Structure As Determined in the Gas Phase by Electron Diffraction, in the Crystalline Phase at 199 K by X-ray Diffraction, and by ab Initio Computations.
The compound 1-phenyl-1,2-dicarba-closo-dodecaborane(12), 1-C(6)H(5)-1,2-closo-C(2)B(10)H(11) (1), has been synthesized and characterized by a complete assignment of its (11)B NMR spectrum via (11)B{(1)H}/(11)B{(1)H} (COSY), (1)H{(11)B(selective)} and (1)H{(11)B}/(1)H{(11)B} (COSY) spectroscopy. An electron- and X-ray diffraction investigation of 1, complemented by ab initio calculations, has been undertaken. The gas-phase electron-diffraction (GED) data can be fitted by several models describing conformations which differ in the position of the phenyl ring with respect to the carborane cage. Local symmetries ofC(2)(v)() and D(6)(h)() for the 1,2-C(2)B(10) and C(6) moieties, respectively, were adopted in the GED model in order to simplify the problem. In addition, constraints among the close-lying C-C and B-B bonds were employed. However, even though such simplifications led to satisfactory refinements (R(G) = 0.069-0.071), a unique, definitive solution could not be gained. The (C-C)(mean), (C-B)(mean) and (B-B)(mean) bond lengths,r(a), are ca. 1.44, 1.72, and 1.78 Å, respectively. The C(6) hexagon, with r(a)(C-C) = ca. 1.394 Å, either eclipses the C(1)-C(2) vector (overall C(s)() symmetry) or more or less eclipses the C(1)-B(4) cluster bond (overall C(1) symmetry). In contrast, in the solid at 199 K, the ring lies at a position intermediate between the two GED positions, as determined by X-ray crystallography [C(8)H(16)B(10), monoclinic P2(1)/a: a = 12.047(3) Å, b = 18.627(4) Å, c = 12.332(5) Å, beta = 110.09(4) degrees, Z = 8]. The C-B distances span the range 1.681(6)-1.743(5) Å, and B-B lengths lie between 1.756(6) and 1.795(6) Å. A similar conformation was found for the theoretical (RHF/6-31G level) structure which was fully optimized in C(1) symmetry. The r(e) distances are consistent with the dimensions derived in the experimental studies. IGLO calculations of the (11)B chemical shifts, in addition to SCF single-point energies of the GED structures, further support these observations.