James A. Kaduk

Crystal and molecular structure of (η3-allyl)carbonylchlorobis(dimethylphenylphosphine)- iridium(III) hexafluorophosphate, [Ir(η3-C3H5)Cl(CO)(P(CH3)2(C6H5))2][PF6

Abstract The structure of (η 3 -allyl)carbonylchlorobis(dimethylphenylphosphine)-iridium(III) hexafluorophosphate, [Ir(η 3 -C 3 H 5 )Cl(CO)(P(CH 3 ) 2 (C 6 H 5 )) 2 ][PF 6 ], has been determined from three-dimensional X-ray data to add support for a proposed mechanism of the oxidative addition of allyl halides to IrX(CO)(PR 3 ) 2 (X = halide). The compound crystallizes in space group C 5 2h - P 2 1 / c with four formula units in a cell of dimensions a = 11.027(1), b = 12.230(2), c = 19.447(5) A, and β = 103.16(2) 0 . Least-squares refinement of the structure has led to a value of the conventional R index (on F ) of 0.066 for the 3018 independent reflections having F 2 0 >3—(F 2 0 ). The crystal structure consists of discrete, monomericions. The hexafluorophosphate anion is disordered. The coordination geometry around the iridium atom may be described as octahedral, with the chloro ligand trans to the carbonyl group and each phosphorus atom trans to a terminal carbon of the allyl group. Structural parameters: Ir—P = 2.366(4), 2.347(3);Ir—Cl = 2.389(3); Ir—C(allyl) = 2.28(1), 2.24(1),2.25(1); Ir—C (carbonyl) = 1.85(1) A; P—Ir—P = 105.7(1); C(terminal)—Ir—C(terminal) = 66.2(8); C—C—C = 125(2) o . The allyl group makes an angle of 126 o with the P—Ir—P plane. Correlations between geometric structure and number of d electrons are noted among several M—C 3 H 5 -complexes, and are interpreted in the light of theoretical models of the M—C 3 H 5 - bond.

Preparation and structure of trans-(η1-allyl)chlorobis(triphenylphosphine)platinum(II), Pt(η1-C3H5)Cl[P(C6H5)3]2

Abstract The structure of trans-(η1-ally)chlorobis(triphenylphosphine)platinum(II), Pt(η1-C3H5)Cl(PPH3)2, has been determined from three-dimensional X-ray data. The compound was isolated while attempting to grow crystals of [Pt(η3-C3H5)(PPH3)2]Cl. The complex crystallizes in the space group C52hue5f8P21/n with four molecules in a unit cell of dimensions a = 12.580(3), b = 23.067(7), c = 12.316(4) A and β = 112.30(1)°. Least-squares refinement of the 136 variables has led to a value of the conventional R index (on F) of 0.048 for the 6289 independent reflections having F2o > 3σ(F2o). The complex is a typical square-planar Pt(II) complex; structural parameters: Ptue5f8P 2.304(2) and 2.302(2), Ptue5f8Cl 2.425(2), Ptue5f8C(1) 2.090(4), C(1)ue5f8C(2) 1.464(7), C(2)ue5f8C(3) 1.311(9) A, Ptue5f8C(1)ue5f8C(2) 112.6(3)°, C(1)ue5f8C(2)ue5f8C(3) 125.7(6)°. The angle between the plane of the allyl group and the mean coordination plane is 66°; the torsion angle Ptue5f8C(1)ue5f8C(2)ue5f8C(3) is −119°. The structure is compared with other Pt(II) σ-complexes, and production of the complex rationalized. The isolation of the complex supports suggestions that the fluxionality of [Pt(η3-C3H5)(PPH3)2]Cl in solution involves a short-lived σ-allyl intermediate.

The [Rh(NO)2(PPh3)2]+ catalyzed reaction 2NO + CO → N2O + CO2

Abstract The reaction 2NO + CO → N 2 O + CO 2 has been found to be catalyzed by [Rh(NO) 2 (PPh 3 ) 2 ] in N,N -dimethylformamide (DMF) solution. The rate expression and thermodynamic quantities found are consistent with a mechanism involving a dirhodium species and DMF.

Catalysis of NO + CO

can be labeled by tritium. The methyl group of thymine for DNA stems from formate, and therefore is not labeled by [methyl-3H]SAM. It can be differentially labeled with [4C]formate. When Scarano found that a portion of the thymine in the DNA of sea urchin embryo which had been incubated with [methyl-3H]methionine bore the tritium label, he concluded that this minor thymine came from the deamination of [methyl-3H]methylcytosine. Indeed, Scarano demonstrated the existence of an enzyme, DNA cytosine deaminase, but this enzyme does not have the ubiquitous occurrence in tissues that would be expected if it had an important regulatory function. The best source of the enzyme is donkey spleen. On the basis of these findings Scarano et al. proposed the synchron model of differentiation (3). The model described by Holliday and Pugh is an extension ofScaranos model. However, there is another pathway possible for the entry of tritium label into the minor thymine of DNA. There is thymine in tRNA as well, but this thymine is synthesized at the polymer level by the addition of an intact methyl group from SAM (4). Should there be a salvage pathway for the thymine resulting from the turnover of tRNA, tritium-labeled thymine might find its way into DNA. Excess thymine in tissues is catabolized to f-aminoisobutyric acid (,AIB), which is excreted in the urine. By taking advantage of the different pathway of synthesis of the thymines in tRNA and DNA, we have been able to show by differential labeling that 3AIB has a dual origin; it stems from the degradation of thymine of DNA as well as thymine of RNA (5). Weber has shown that in rapidly growing tumor tissue the catabolic degradation of thymine to ,BAIB is greatly diminished (6). We have confirmed his in vitro observation by in vivo experiments. The excretion of ,AIB stemming from both DNA and RNA by rats with rapidly growing Novikoff hepatoma diminishes. In turn, in those rats injected with [methyl-3H]methionine, the tritium in thymine of DNA in the tumor tissue is significant, approximately 5 percent of the total thymine (7). This may stem from the deamination of 5-methylcytosine in DNA or from a salvage of tritium-labeled thymine from tRNA. The concomitant diminution of the excretion of ,BAIB suggests, but does not prove, the existence of such a salvage pathway. Holliday and Pugh invoke a number of reversible modification mechanisms of DNA: two different DNA deaminases, two different DNA reaminases, DNA demethylases, and DNA methylases. Of