Element−Element Bonds. IX.¹ Structures of Tetrakis(trifluoromethyl)diphosphane and -diarsane:  Experimental and Theoretical Investigations

Abstract

X-ray structure determinations of tetrakis(trifluoromethyl)diphosphane (2c, mp -82 degrees C, triclinic, P&onemacr;; Z = 1, a = 529.7(3) pm, b = 681.6(2) pm, c = 802.8(3) pm, alpha = 108.58(1) degrees, beta = 99.66(1) degrees, gamma = 103.29(1) degrees, wR2 = 0.204) and -diarsane (3c, mp -52 degrees C, monoclinic, P2(1)/c; Z = 2, a = 769.5(3) pm, b = 750.0(3) pm, c = 960.7(2) pm, beta = 105.26(1) degrees, wR2 = 0.115), both at -100(3) degrees C, reveal the molecules to adopt the trans conformation in the solid. Compared with the tetramethyl derivatives, the E-E (224.6(2)/246.3(1) pm, E = P, As) and E-C (188.3(4)/201.3(7) pm) bonds are elongated by 4.5/4.8 pm and 3.4/3.4 pm, respectively. From gas electron diffraction studies of diphosphane 2c a mixture of 85(10)% trans and 15(10)% gauche conformers can be deduced; diarsane 3c shows the trans form exclusively. The molecular parameters (E-E, 224.8(11)/245.2(6); E-C, 189.6(4)/ 201.2(4) pm) agree excellently with those determined for the crystalline state. As a result of quantum chemical calculations at Hartree-Fock and hybrid density functional levels of theory using 6-311+G basis sets, the gauche conformer of hydrazine derivative 1c and the trans conformer of diarsane 3c are clearly lowest in energy. However, for diphosphane 2c the gauche and not the trans form is found to be slightly more stable. Variations of calculated E-E and E-C bond lengths are analyzed and compared with corresponding values of the parent compounds E(2)H(4) (1a to 3a) as well as the tetramethyl derivatives 1b to 3b.

PP-Rotation, P-Inversion and Metathesis in Diphosphines Studied by DFT Calculations: Comments on Some Literature Conflicts

“…A destabilising effect is also observed for the anti conformer and apparent in a local elongation of the P-P bond length. The P-P bond length of the gauche conformers of 3 (2.263 Å) is in closer agreement with the literature data, 2.246 Å (X-ray of solid), 2.25 Å (electron diffraction) [22] and 2.259 Å (calculations at the B3PW91/aug-cc-pVTZ level) [23].…”

“…Cowley, et al attributed signals in the photoelectron spectrum of tetramethyldiphosphine, 2, and tetrakis-(trifluoromethyl)diphosphine, 3, to anti and gauche rotamers [25] while Becker, et al more recently studied the same compounds using gas phase electron diffraction [22]. Boltzmann distributions calculated from the rotational energy profiles presented here are in close agreement with the values reported from the photoelectron spectrum of 2 but are significantly different in the case of 3, summarised in Table 3.…”

“…The P-P bond length is overestimated for both 1 (2.252 and 2.268 Å for gauche and anti, respectively) and 2 (2.244 and 2.254 Å for gauche and anti, respectively), whose bond lengths have been measured at 2.219 Å (gas electron diffraction) and 2.212 Å (X-ray diffraction), respectively [21,22]. Azofra, et al also obtained the P-P distance for 1-gauche (2.220 Å) at the MP2/aug-cc-pVTZ computational level [20], while Katsyuba et al [23] performed calculations of H 4 P 2 and Me 4 P 2 at different computational levels, HF/aug-cc-pVTZ, B3PW91/aug-cc-pVTZ and BPW91/cc-pVTZ finding P-P distances of 2.422 and 2.231 Å for 1 and 2 respectively at the most accurate level (B3PW91/aug-cc-pVTZ).…”

Strategies for the synthesis of chiral, bidentate bis(perfluoroorganyl)phosphane ligands

“…The reduced electron density of the phosphorus atom in the [P(CF 3 ) 2 CS 2 ] À ion reduces the negative hyperconjugation [63]. Therefore, the P-C and C-F bond lengths are comparable to those of neutral trifluoromethylphosphanes such as (CF 3 ) 2 PP(CF 3 ) 2 [64]. In [K(18-crown-6)] [P(CF 3 ) 2 CS 2 ] as well as in K[P(CF 3 ) 2 CS 2 ], n as (CS 2 ) and n s (CS 2 ) lie close to the positions previously reported for K[PPh 2 CS 2 ] [65].…”

Synthesis and molecular structures of dinuclear complexes with 1,2-dihydro-1,2-diphenyl-naphtho[1,8-c,d]1,2-diphosphole as a bridging ligand

“…The relative instability of cis-1 is mainly due to a steric repulsion between the two phenyl groups disposed at the same side with respect to the naphthalene plane. In addition, a repulsive interaction is also expected between two lone pairs on the phosphorus atoms of cis-1, although it is reported to be faint owing to a significant s character of the lone pair on the phosphorus [13,14]. Such steric and lone pair repulsions are absent in trans-1, as is evident in Fig.…”