Synthesis, characterization, low-temperature (50 K) neutron diffraction structure, and reactivity of chlorodihydridotetrakis(trimethylphosphine)tantalum(III)

Abstract

Dichlorodihydridotetrakis(trimethylphosphine)tantalum(IV), TaCl2H2(PMe3)4, is reduced under argon by sodium amalgam in the presence of PMe3 to give green TaClH2(PMe3)4 (la) in 70% yield, la has been characterized by IR spectroscopy, variable-temperature and 31P('H) NMR spectroscopy, and low-temperature (50 K) neutron crystallography. In the solid state, la is a slightly distorted pentagonal bipyramid with two axial phosphines. The hydride ligands are coordinated in a cis configuration in the pentagonal plane with a H-Ta-H angle of 66.2 (6)°a nd Ta-H distances of 1.79 (1) and 1.80 (1) A. la reacts readily with Me2PCH2CH2PMe2 (dmpe) to give TaClH2(dmpe)2 (2) and with ethylene to give TaCl(C2H4)(PMe3)4 (3). It also reacts with dinitrogen to given the µ-dinitrogen complex [TaClH2(PMe3)3]2(M-N2) (4a) and with carbon monoxide to provide TaCl-(CO)3(PMe3)3 (5). The latter complex has been characterized by low-temperature (-160 °C) X-ray crystallography. In the solid state, 5 is a capped (by Cl) trigonal prism with three PMe3 ligands and one CO on the capped quadrilateral face and two CO ligands on the remaining edge. Crystal data are as follows: for la (at 50 K), monoclinic space group P2\/a, a = 18.436 (4) A, b = 9.139 (2) A, c = 12.376

Distance and Scalar HH-Coupling Correlations in Transition Metal Dihydrides and Dihydrogen Complexes

“…We will show that this concept reproduces not only the structural changes but also the magnetic couplings between the two hydrogen nuclei in a wide range of r HH values. This problem has been the subject of several experimental 6,7j,n,8 and theoretical 9 studies; however, so far a linear correlation was assumed, which is only valid in the range of short dihydrogen distances. 6c,7n …”

“…To check validity of eq 5, we performed a search for neutron diffraction structures of transition metal dihydrides and dihydrogen complexes. We found 16 neutron structures 7a-p in the Cambrige Structural Database (CSD) 10 and W(PMe 3 ) 4 H 2 Cl 2 ( 17 ) and W(PMe 3 ) 4 H 2 F(FHF) ( 18 ) in ref q. We included compounds with additional hydrogen ligands only if they were immobile and part of a bridge to another metal.…”

“…The solid line was calculated using eq 5 as described in the text. Dihydrides (CSD codes, version 5.15): BOPJUL ( 1 ), 7a,b BORFOD10 ( 2 ),7c BUXFIJ01 ( 3 ),7d CIWJAT10 ( 4 ),7e CONFEQ01 ( 5 ),7f DECVAI01 ( 6 ),7g DECVEM01 ( 7 ),7h GEVNIE05 ( 8 ),7h HCYPMO02 ( 9 ),7i JOLWAI01 ( 10 ),7j OHEPRH01 ( 11 ),7k PESFOI ( 12 ),7l PIYGAF ( 13 ),7m TEQMIL ( 14 ),7n WADSAV ( 15 ),7o ZEGZAM01 ( 16 ),7p no codes ( 17 , 18 ) 7q. Trihydrides: GATDOU01 ( 19 ),11a TACPTH ( 20 ) 11b.…”

“…Lower dotted line: second term of eq 6. Experimental values: J HD = 43 Hz (free HD), 34 Hz ( 1 ),7b 34 Hz ( 15 ),7o 21.5 Hz ( 10 ),7j 13.6 Hz ( 14 ),7n 9.1 Hz ( 13 );7m J HT = 27.3 Hz ( 19 );11c J HH = 9.5 Hz ( 20 ),11d −5.6 Hz ( 21 ),15a −6.1 Hz ( 22 ),15b −8.5 Hz [RuH 2 {η 4 -HSiMe 2 (CHCHMe)}(PCy 3 ) 2 ( 23 )],15c −18.2 Hz ( trans -FeH 2 -( meso -tetraphos-1) ( 24 ) 15d. For complexes with r HH > 2.0 Å, negative signs for the scalar magnetic coupling constants were assumed. …”

Isotope and Nuclear Chemistry Division annual report FY 1989, October 1988--September 1989

“…Further details of the chemistry of 1 are available in three of our publications. 88 High-level radioactive waste consists primarily of fission products and actinide elements: the acUnide elements neptunium, plutonium. and amerii'iuni constitute a long-term hazard because of their relatively long half-lives and high radioactivity.…”