Inorganica Chimica Acta 262 (1997) 21–32 0020-1693/97/$17.00 q 1997 Elsevier Science S.A. All rights reserved PII S0020-1693 ( 97 ) 05492-3 W 2 Cl 4 (NR 2 ) 2 (PR9 3 ) 2 molecules 6. New triply-bonded ditungsten complexes with bis(diphenylphosphino)methane or bis(diphenylphosphino)amine as a bridging ligand. Crystal structures of cis,cis-W 2 Cl 4 (NR 2 ) 2 (dppm) (RsEt, Bu n ) and W 2 Cl 3 (NHCMe 3 ) 2 (NH 2 CMe 3 )(PPh 2 NPOPh 2 ) F. Albert Cotton a,U , Evgeny V. Dikarev a , N. Nawar b , Wai-Yeung Wong a a Department of Chemistry and Laboratory for Molecular Structure and Bonding, Texas A&M University, College Station, TX 77843-3255, USA b Chemistry Department, Faculty of Science, Mansoura University, Mansoura 35516, Egypt Received 31 October 1996 Abstract The reactions of W 2 Cl 4 (NR 2 ) 2 (NHR 2 ) 2 (RsEt, Bu n ) with a stoichiometric amount of bis(diphenylphosphino)methane (dppm) readily resulted in the isolation of two new triply-bonded ditungsten(III) compounds cis,cis-W 2 Cl 4 (NR 2 ) 2 (dppm)(RsEt (1),RsBu n (2)) in moderate yields. The molecular structures of both compounds have been determined by X-ray crystallography and their crystallographic data are as follows: 1PCH 2 Cl 2 , monoclinic, space group C2/c, as38.729(5), bs11.662(1), cs19.045(2) A ˚ , bs113.57(1)8, Vs7884(2) A ˚ 3 , Zs8, Rs0.026, wR2s0.055; 2, monoclinic, space group P2 1 /n, as14.4962(5), bs18.6305(8), cs17.1667(6) A ˚ , bs97.974(4)8, Vs4591.4(3) A ˚ 3 , Zs4, Rs0.043, wR2s0.102. Both molecules are characterized by a W 2 6q core with a s 2 p 4 bond of order three and the W–W distances are 2.3350(3) and 2.3463(4) A ˚ , respectively, for 1 and 2. They entail an essentially staggered rotational geometry and exhibit significant torsion angles in the solid state. Similar procedure has also been used to prepare similar W 2 6q complexes containing bis(diphenylphosphino)amine (dppa) ligands and complexes of the type W 2 Cl 4 (NR 2 ) 2 (dppa)(RsEt (3),RsBu n (4)) have been characterized by 31 P{ 1 H} NMR spectroscopy at room temperature. In leading to the reaction pathway of complexes of this kind, the time sequences for the formation of 1 and 2 have been followed by variable temperature 31 P{ 1 H} NMR spectroscopic method. In all cases, the trans,trans-isomers of W 2 Cl 4 (NR 2 ) 2 (L–L)(RsEt, Bu n ; L–Lsdppm, dppa) are the kinetically favored products while the cis,cis-isomers are the thermodynamic products. The corresponding cis,trans compounds are believed to be the likely intermediate complexes. In the course of a synthetic program directed towards the preparation of a dppa substitution complex of W 2 Cl 4 (NHCMe 3 ) 2 (NH 2 CMe 3 ) 2 , an unexpected ditungsten compound W 2 Cl 3 (NHCMe 3 ) 2 (NH 2 CMe 3 )(PPh 2 NPOPh 2 )(5) has been prepared and structurally characterized. Compound 5 crystallizes in the triclinic space group , as11.269(2), bs12.020(5), cs18.182(2) A ˚ , as93.27(1), bs89.72(1), gs93.275(2)8, # P1 Vs2455(1) A ˚ 3 , Zs2, Rs0.068, wR2s0.153. The W–W distance in 5 is 2.3030(8) A ˚ and the molecule consists of an anionic bridging ligand [N(OPPh 2 )PPh 2 ] y , forming a six-membered metallacycle with the ditungsten unit. Keywords: Crystal structures; Ditungsten complexes; Bis(diphenyphosphino)methane complexes; Bis(diphenylphosphino)amine complexes 1. Introduction Triply-bonded ditungsten compounds of the types W 2 Cl 4 (NHR) 2 (L–L) and W 2 Cl 4 (NR 2 ) 2 (L–L), where L–L is a bridging bidentate phosphine, have been extensively stud- ied recently in this laboratory [1,2]. The properties of these compounds depend on the nature of the amido groups present and both the p-acidity and the steric requirement of the diphosphines used. U Corresponding author: Tel.: q1 409-845 4432; fax: q1 409-845 9351. While the ligands bis(diphenylphosphino)methane (dppm) and bis(diphenylphosphino)amine (dppa) are well- known for their ability to act as bridging ligands in dinuclear complexes of Mo or Re [3], there are relatively few data for W 2 species having these ligands [4]. To our knowledge, no structurally characterized example is yet available for dppm and dppa complexes of the W 2 6q unit. We would like to report here the successful preparation and structural charac- terization of two bridging dppm complexes of ditung- sten(III), viz. the cis,cis-isomers of W 2 Cl 4 (NEt 2 ) 2 (dppm) (1) and W 2 Cl 4 (NBu n 2 ) 2 (dppm)(2), and in addition the