Showing papers by "George M. Whitesides published in 1969"

Reaction of copper(I) hydride with organocopper(I) compounds

Abstract: A number of important transition metal catalyzed organic syntheses are carried out in solutions containing mi,rtures of intermediate transition metal hydrides and a-alkyls.3 The reactivity of transition metal hy-drides toward metaI alkyls has not been defined. However , the facility with which nontransition metal hy-rides react with many o-organometallic compoundsi,r suggests that analogous reactions of transition metal hydrides might be important in the catarytic transition metal systems. As part of a study of the mechanism(s) of thermal decomposition of copper(l) alkyis, we have prepared cop-per(l) hydride and examined its reactivity toward oi-ganocopper(l) compounds. The reactivity of copper hydride toward copper alkyls is of particurar inrerest as a model for the reactivity of other transition metal hy-drides and alkyls: since copper hydride does not cata-lyze olefin isomerization or deuterium exchange under the conditions used in this study, the structures of hydrocarbon products formed in the presence of copper hydride can be determined without ambiguity. Here we wish to report that hydridic and o-organometallic derivatives of copper(t) react readily with one another, and that the mechanism of this reaction does not involve intermediate organic free radicals.-Copper(t) hydride was prepared by treating I equiv of copper(l) bromide dissolved in 100 equiv oipyri,iine with l.l equiv of diisobutylaluminum hydriAe (j0 % in heptane) rt-50o. Vigorous mixing produced a homogenous , dark brown solution, from which copper(l) hydride could be precipitated by dilution with .-300 equiv of ether. centrifugation, separation of the super-natant liquid, and repeated washing of the precipitatc with ether, all at-78o, permitted isolation of copper(l) hydride as a brown solid in greater than 90% yielci.; The ratio oi hydride to copper in this material is 0.96 * 0.0,1; it contains less than 0.5% aluminum or bromine but retains-25 /, pyridine, based on copper. Pure, anhydrous copper(l) hydride decomposes ro hydrogen and metallic copper above-20o; it is indefinitely stable at-78o. Suspensions of copper(l) hydride in ether are relatively air insensitive; the dry solid is pyrophoric. Tri-rr-butylphosphine and cop-per(l) hydride form a I : I complex, the high solubility ofi which has prevented its isolation. Attempts to detect a metal-hydrogen stretching vibration in the solLr-tion ir spectrum of copper hydride, or a hydride resonance in its nmr spectrum, have so far been unsucces-ful.3 Hydrido(tri-n-butylphosphine)copper(l) reduces primary , secondary, and tertiary alkyl-, vinyl-, and aryl-copper(l) compounds to the corresponding hydrocar-(2) For reviews of rcpresentative rcactions, see R. Heck, Adcan. (5) This procedure is bascd on …

Vanadium nuclear spin-lattice relaxation in .pi.-tropyliumvanadium(-I) tricarbonyl

Abstract: 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