Abstract
The compound [Rh(Hdmg)2(PPh3)]– ([Rh]–), synthesized by reduction of [Rh]–Cl with NaBH4 in methanolic KOH, reacted with 1,2-disubstituted ethanes XCH2CH2X′ (X/X′ = Cl/OMe or Br/Br) forming [Rh]–CH2CH2OMe 1a as well as [Rh]–Br and ethylene as heterolytic fragmentation products. Heterolytic fragmentation of 1a enforced by protonation with acids (CF3SO3H, CD3CO2D) generated MeOH, H2CCH2 and [Rh]–O3SCF3 and [Rh]–O2CCD3, respectively. Reaction of [Rh]– with XCH2CH2X′ (X/X′ = Cl/Cl, Cl/Br or Cl/OPh) afforded the dinuclear complex [Rh]CH2CH2[Rh] 2a. The anion [Rh]– reacted with Cl(CH2)3Cl to give [Rh]–CH2CH2CH2Cl 1b, whereas Br(CH2)3Br was reacted with excess and equimolar amounts of [Rh]–, yielding [Rh]CH2CH2CH2[Rh] 2b and [Rh{(CH2)3ON C(Me)C(Me)NO}(Hdmg)(PPh3)] 3b, respectively. Similar reactions carried out with Br(CH2)nBr (n = 4 or 5) yielded [Rh]–(CH2)5Br 1d, [Rh](CH2)n[Rh] (n = 4 2c or 5 2d) and [Rh{(CH2)nON C(Me)C(Me)NO}(Hdmg)(PPh3)] (n = 4 3c or 5 3d), respectively. All complexes were fully characterized by NMR spectroscopy (1H, 13C, 31P). The 31P-{1H} NMR spectra of dinuclear complexes 2a and 2b exhibit typical AA′ patterns of AA′XX′ systems (A = 31P, X = 103Rh) due to considerable 5J(31P–31P) and 6J(31P–31P) couplings (36.7, 11.2 Hz), respectively. The crystal structures of the dinuclear rhodoximes 2a–2c and of the cyclic organorhodoxime 3b have been determined. The two (Hdmg)2 planes in the di- and tetra-methylene-bridged complexes 2a and 2c are parallel with distances of 4.5 (2a) and 7.1 A (2c), respectively, and exhibit an ecliptic conformation. In the trimethylene-bridged complex 2b, the two (Hdmg)2 planes include an angle of 45.0(1)° and exhibit a staggered conformation, which minimizes electrostatic repulsion between the O–H–O moieties and the steric interference between two methyl groups. In 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 in the O–H–O bridge [O(2)· · ·O(3) 2.58(1) A] is distinctly shorter than those that are not connected via a hydrogen bridge [O(1)· · ·O(4) 3.30(1) A].
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