Dihydrogen Complexes

Question 1

type of ligand

Answer 1

L, e- donation from H-H sg BMO

Question 2

M-H2 interactions

Answer 2

H2 sg depopulated but not enough to break H-H bond, pi-back donation to su* limited giving greater stability of LM t2g orbital meaning H2 can bind to MC and stay intact

Question 3

normal dihydrogen

Answer 3

e- poor MC with weak pi-back donation from ligands, gives free rotation of H2 at RTP

Question 4

stretched dihydrogen

Answer 4

longer H-H with intermediate pi-back donation

Question 5

dihydride

Answer 5

more e-rich MC, strong pi-back gives H-H cleavage

Question 6

characterisation of dihydrogen complexes

Answer 6

SXRD = hard to locate small H atoms
vibrational spectroscopy = weaker H-H gives lower stretching freq but this isnt always seen
H NMR spectroscopy = can prepare HD complexes and measure coupling constant

Question 7

H2 elimination

Answer 7

dihydrogen weakly bound meaning easy dissociation giving unsaturated LnM

Question 8

oxidative cleavage of dihydrogen

Answer 8

dihydrogen close in energy to dihydride, can interconvert via oxidative cleavage and reductive coupling

Question 9

heterolytic cleavage of dihydrogen

Answer 9

e- deficient metal means s-donation dominates, gives net flow of e- density from H2 sg to MLn s ornital, H2 ligand becomes acidified making it more easily deprotonated wrt free H2