The crystal and molecular structure of 1,4-diphenyl-2,2′,3,3′,5,5′,6,6′-octamethylcyclo-1,4-diphospha-2,3,5,6-tetrasilahexane, a phosphorus–silicon heterocycle

Abstract

A. WALLACE CORDES, PALL F. SCHUBERT, and RICHARD T. OAKLEY. Can. J. Chem. 57, 174 (1979).The crystal structure of 1,4-diphenyl-2,2',3,3',5,5',6,6'-octamethylcyclo-l,4-diphospha-2,3,5,6-tetrasilahexane, (PhPSi2Me,),, has been determined by single crystal X-ray diffraction. The crystals are monoclinic, space group P2,!c, with a = 9.866(1), b = 11.921(1), and c = 11.324(2) a, e = 104.31(1)", Z = 2, and p,,,,, = 1.15 g'cm3. The structure was solved by direct methods and was refined by full-matrix least-squares procedures to a final R of 0.060 and R, of 0.078, for 1173 reflections uith intensities greater than 30. The (PhPSi,Me4), molecule lies on a crystallographic centre of symmetry, and the six-membered P2Si, ring has a chair conformation with equatorial phenyl groups. The endocyclic angles at P (104.4(1)") and Si (104.9(2)') are intermediate between those found in cyclic hexaphosphine and hexasilane molecules, and the Si-Si and P-Si distances of 2.345(3) and 2.252(4) A, respectively, correspond to single bond lengths, with no appreciable evidence for secondary prt + drt bonding between phosphorus and silicon. The Si-C (1.867(8) A) and P-C (1.828 (7) Faisant appel a la diffraction des rayons X par des monocristaux, on a d6terniini. la structure cristalline du diphenyl-1,4 octamethyl-2,2',3,3',5,5',6,6' cyclodiphospha-1,4 tktrasilahexane-2,3,5,6, (PhPSi,Me,),. Les cristaux sont monocliniques, groupe d'espace P2Jc avec n = 9.886(1), b = 11.921(1) et c = 11.324(2) A, = 104.31(1),Z = 2 e t p ,,,,, = 1.15 g/cm3. On a resolu la structure par des methodes directes et on l'a affinee par la methode des moindres carres (matrice complete) jusqu'a une v a l e~~r finale R de 0.060 et R , de 0.078 pour les 1173 riflexions avec des intensites plus grandes que 30. La molecule (PhPSi,Me,), se trouve au centre de syrnetrie et le cycle a six chainons P2Si, adopte une conformation chaise avec les groupes phenyles en position equatoriale. Les angles endocycliques au niveau du P (104.4(1)") et du Si (104.9(2)') sont intermediaires entre ceux trouves dans des molecules d'hexaphosphines et d'hexasilanes cycliques et les distances Si-Si et P-Si qui sont respectivenient 2.345(3) el 2.252(4) A correspondent a des longueurs de liaisons simples el I'on ne trouve aucune indication a I'effet qu'il existe une liaison secondaire prt + r/rt entre le phosphore et le silicium.

The crystal and molecular structure of the molybdenum tetracarbonyl complex of 1,4-diphenyl-2,2′,3,3′5,5′,6,6′-octamethylcyclo-1,4- diphospha-2,3,5,6-tetrasilahexane

“…The axial carbonyl groups are bent away from the perpendicular (C,,-Mo-C,, = 164.2(2)"), presumably to relieve possible steric crowding from the bulky phosphasilane ligand. Similar distortions, of varying magnitude, are observed in other diphosphine molybdenum tetracarbonyls (6,(17)(18)(19)(20)(21). Again as elsewhere, the axial and equatorial Mo-C bonds are of unequal length (Table 6), the shorter equatorial bonds reflecting the increased n-back-donation from the metal to the carbonyl groups trans to the phosphine ligand.…”

“…The P-Mo bonds (mean length 2.592(15) A)9 are significantly longer than in other phosphine molybdenuin carbonyls (2.37-2.53 A) (6,(17)(18)(19)(20)(21)23), and we believe that the lengthening, which is observed to a lesser extent in (PhPHSi,Me,PPhH)Mo(CO), (3), is the result of a cumulative reduction in n-backbonding from molybdenum to phosphorus caused by the low electronegativity of silicon and the consequent polarity of the P-Si bonds. Consistently, the carbonyl stretching frequencies of I1 are slightly but significantly lower than in related compounds ( Table 6).…”

“…The mean P-Si distance (2.275(19) A) is longer than in the uncomplexed structure (2.252(4) A), and, even though hybridization changes would tend to accentuate the difference, the lengthening is too small to be definitely ascribed to a px-dx contraction in the latter. There have been several recent structural reports (3,6,10,(11)(12)(13) phorus bonds, as well as electron diffraction studies on simple silylphosphines (14,15), and the range of P-Si bond lengths in all these molecules (see Table 5) provides no clearcut difference between the molecules containing three-and four-coordinate phosphorus atoms. The discrepancy between the apical and basal P-Si bonds in P,(SiMe,), (11) and between the bonds to the bridging and non-bridging phosphorus atoms in (Me,Si),P,(CMe,), (12) For personal use only.…”

“…Figure 2 gives an alternative view, and illustrates the boat conformation of the six-membered P2Si4 ring. The cyclic (PhPSi2Me4), ligand (I), which exists in a chair conformation with equatorial phenyl groups when uncoordinated (6), is forced to adopt the boat conformation upon coordination to molybdenum. As a consequence, there are several angular changes.…”

New Group 14 Element Substituted Phosphaalkenes

“…In the literature, a few disilane bridged diphosphanes are known, for example HypP(H)–Si 2 Me 4 –P(H)Hyp and several cyclic or metalated compounds . The P–C NHC bond in 3 [175.1(2) pm] is nearly as long as in 1 and 2 , the P–Si bond length of 224.2(1) pm is in between the ones observed for 1 and 2 and almost identical to the P–Si distance in the sterically stressed compound HypP(H)–Si 2 Me 4 –P(H)Hyp (224.0(5) pm) .…”