SYNTHESES AND STRUCTURES OF NOVEL CYCLIC AND DINUCLEAR ORGANORHODOXIMES - A HOMOLOGOUS SERIES OF DI-METHYLENE-BRIDGED TO PENTA-METHYLENE-BRIDGED COMPLEXES

The compound [Rh(Hdmg)(2)(PPh3)](-)([Rh](-)), synthesized by reduction of [Rh]-Cl with NaBH4 in methanolic KOH, reacted with 1,2-disubstitut ed ethanes XCH2CH2X' (X/X' = Cl/OMe or Br/Br) forming [Rh]-CH2CH2OMe 1 a as well as [Rh]-Br and ethylene as heterolytic fragmentation product s. Heterolytic fragmentation of la enforced by protonation with acids (CF3SO3H, CD3CO2D) generated MeOH, H2C=CH2 and [Rh]-O3SCF3 and [Rh]-O2 CCD3, respectively. Reaction of [Rh](-) with XCH,CH,X' (X/X' = Cl/Cl, Cl/Br or Cl/OPh) afforded the dinuclear complex [Rh]CH,CH,[Rh] 2a. The anion [Rh](-) reacted with Cl(CH2)(3)Cl to give [Rh]-CH2CH2CH2Cl 1b, whereas Br(CH2)(3)Br was reacted with excess and equimolar amounts of [Rh](-), yielding [Rh]CH2CH2CH2[Rh] 2b and [Rh{(CH2)(3)ON=C(Me)C(Me)=N O}(Hdmg)(PPh3)] 3b, respectively. Similar reactions carried out with B r(CH2)(n)Br (n = 4 or 5) yielded [Rh]-(CH2)(5)Br Id, [Rh](CH2)(n)[Rh] (M = 4 2c or 5 2d) and [Rh{(Ch(2))(n)ON=C(Me)C(Me)=NO }(Hdmg)(PPh3)](n = 4 3c or 5 3d), respectively. All complexes were fully characterized by NMR spectroscopy (H-1, C-13, P-31). The P-31-(H-1} NMR spectra of dinuclear complexes 2a and 2b exhibit typical AA' patterns of AA'XX' s ystems (A = P-31, X = Rh-103) due to considerable (5)J(P-31-P-31) and (6)J(P-31-P-31) couplings (36.7, 11.2 Hz), respectively, The crystal s tructures of the dinuclear rhodoximes 2a-2c and of the cyclic organorh odoxime 3b have been determined. The two (Hdmg)(2) planes in the di-an d tetra-methylene-bridged complexes 2a and 2c are parallel with distan ces of 4.5 (2a) and 7.1 Angstrom (2c), respectively, and exhibit an ec liptic conformation. In the trimethylene-bridged complex 2b, the two ( Hdmg), planes include an angle of 45.0(1)degrees and exhibit a stagger ed conformation, which minimizes electrostatic repulsion between the O -H-O moieties and the steric interference between two methyl groups. I n all three complexes the oligo-methylene bridges are fully staggered. In 3b the six-membered ring(1-oxa-2-aza-3-rhodacyclohexane) exhibits a distorted chair conformation. The distance between the two O atoms i n the O-H-O bridge [O(2)... O(3) 2.58(1) Angstrom] is distinctly short er than those that are not connected via a hydrogen bridge [O(1)... O( 4) 3.30(1) Angstrom].