I+-ABSTRACTION VERSUS I--DISPLACEMENT IN THE REACTIONS OF DIIODOACETYLENE WITH METAL-CARBONYL ANIONS - X-RAY STRUCTURE OF [(OC)5MNC=CMN(CO)5]

Solid diiodoacetylene, IC=CI, reacts with THF solutions of the highly basic, third row, metal carbonyl anion, Re(CO)5-, exclusively by a formal I+-abstraction process producing ReI(CO)5 and Re2I2(CO)8. Under the same conditions, the less basic, first row, metal carbonyl anion, Mn(CO)5-reacts to produce not only Mn2I2(CO)8 by formal I+-abstraction but also (OC),MnC=CMn(CO)5 by I--displacement. These results may bc rationalized by HSAB arguments and consideration of charge distribution in the substrate as indicated by molecular orbital calculations. The X-ray structure of (OC)5MnC=CMn(CO)5 is reported. Crystals are triclinic, space group P1BAR, with Z-1 in a unit cell of dimensions a 6.421(2), b 6.425(2), c 9.520(2) angstrom, alpha-81.86(2), beta-88.55(2), gamma-82.06(2) degrees, and D(calc) 1.79 g cm-3. The structure was solved by the Patterson and Fourier methods and refined by full-matrix least squares to R = 0.024, R(w) = 0.033 for 1372 observed reflections with F(o)2 > 3.0-sigma (F(o)2). The complex is centrosymmetric and thus exhibits an eclipsed geometry in the solid state.