Vanadium Nuclear Spin,Lattice Relaxation in pi,Tropyliumvanadium( - I) Tricarbonyl

The rH nmr spectrum of zr-tropyliumvanadium( I) tricarbonyl (1) at 30' in nonviscous solutions is a broad doublet; in viscous solut ions the spectrum is a relat ively sharp singlet. The temperature dependence of this spectrum in toluene-dr and its viscosity dependence in mixturis of ciclooctane and Nujol establish that the observed spectral l ine shapes in nonviscous media are due to 5rV-rH spin-spin coupling. Combination of the value for the vanaclium spin-littice relaxation time inferred from the rH linl shape of 1 in cyclooctatre solution at 30o with an estimate of its rotational correlation time under these circumstances leads to an approximate value for the vanadium quadru' pole coupling constant in I of (e'zqQlh) = Z.O * 0.5 MHzT\ Tmr invest igat ions of the dynamics of metal atom l \ m ic ra t ion be tween carbon a toms in l lux iona l 1rand -o-C,H" metal complexes have led to the discovery of a var iety of new types of structural ly signi f icant molecular rearrangl3 ments.3 Tire spectral data on which these studies are based, al though widcly var iegated, have normal ly shared one feature in common: L , i z . , the re la t i ve ly compiex "s low-exchange" Spectra obser l ,ed at low ternperatures become simpler o i h igh . , tempera tures , as the magnet ic nonequ iva lences charac ter iz ing the s ta t i c s low-exchange St ruc tures are averaged. The tempera ture dependence o f the nmr spec t rum o [ a . r ropy l iumvanad iunr ( l ) t r i carbony la (1 ) descr ibed by Fr i t z and Kre i te r appeared to p rov ide a no tab le e iccp t ion to th is genera l pa t te rn o f behav io r :3 the singie sharp peak observed for 1 at 50o in to luene