D0128

STRUCTURES OF [trans-M(H)(H2)(dppe)2]+, M=Fe,Ru,Os, BY SINGLE-CRYSTAL NEUTRON DIFFRACTION.* J. Ricci1,2, A. Albinati3, J. Fortin1,2, W. Klooster1, T. Koetzle1, P. Maltby4, R. Morris4, A. Petroff4, Depts. of Chem., Brookhaven Nat. Lab., Upton, NY 11973 USA, Univ. S. Maine, Portland, ME 04103 USA, and Univ. Toronto, Toronto, Ontario M5S 1A1 Canada; and Inst. of Pharm. Chem., Univ. Milan, I-20131 Milan, Italy

Activation of the H2 ligands in the d6-octahedral series [trans-M-(H)(H2)-(dppe)2]+, M= Fe(1), Ru(2), Os(3), is shown to increase in the order Fe~Ru<Os, based on neutron diffraction and NMR. The H2 activation step, which results from M([[pi]])-H2([[sigma]]*) backbonding with concomitant lengthening of the H-H bond, is of central importance in a number of catalytic processes. H2 complexes have been the subject of intense interest ever since their discovery over 10 years ago by Kubas5 because of their relevance as models for H2 activation, and their many novel properties including quantum exchange. Essential results from our neutron diffraction studies of 1 BPh4, 2 BPh4, and 3 BF4 are now given in the Table together with some NMR information on the complexes in solution. It is apparent that the neutron bond distances, d(H-H), are systematically foreshortened relative to the NMR-derived values which are discussed elsewhere6. Therefore it is essential that the neutron distances be corrected for librational motion, and we have attempted to do this based on rigid-body models. The corrections result in much improved agreement for all three complexes.

Table of Neutron Results, and NMR data for 1 BPh4, 2BPh4 and 3 PF6[[section]] 

Complex                    Neutron Diffraction  NMR           
            Temp.,K      d(M-H)       d(M-H2)+  d(H-H)   dcorr                          
(H-H)  J(H,D),Hz  d(H-H)                                                                
 1     20       1.54(1)  1.62(1)  0.82(2)  0.85     30.8     0.87     
2      12       1.64(2)  1.81(2)  0.82(3)  0.94     32.4     0.90     
3      13       1.62(1)  1.75(2)  0.79(1)  0.96     25.5     1.02     
       57       1.60(2)  1.78(4)  0.78(2)                             
       100      1.62(2)  1.75(4)  0.72(4)
[[section]]Distances in Ångstroms with esd's in parentheses. +Mean value.

*Work performed under contract DE-AC02-76CH00016 with the US DOE, Office of Basic Energy Sciences.

1Brookhaven. 2S. Maine. 3Milan. 4Toronto.

5Kubas, G. J. Acc. Chem. Res. 1988, 21, 120.

6Bautista, M. T.; Cappellani, E. P.;Drouin, S. D.; Morris, R. H.; Schweitzer, C. T.; Sella, A.; Zubkowski, J. J. Am. Chem. Soc. 1991, 113, 4876.