3508
The seven examples cited here would seem to offer some convincing evidence in support of the mechanism given in eq. 2 for the reaction between NO and vinyl and substituted vinyl radicals a t room temperature. Furthermore, starting with the alkyne, reactions 1 and 2 appear to define a new structurally specific route for the scission of carbon-carbon triple bonds. Further work is in progress in this laboratory on the kinetics of the reactions herein described, on the applicability of the proposed mechanism to alkynyl and vinyl structures in general, and on the properties of the intermediate formed between the vinyl radical and nitric oxide. Acknowledgment.-The authors express their deep appreciation to Dr. 0. P. Strausz and Dr. A . J. Yarwood for many helpful discussions. DEPARTMEST OF CHEMISTRY UNIVERSITY O F ALBERTA
L’ol. 85
COMMUNICATIONS TO THE EDITOR
‘‘0°/ 320.0 e 322.5 9 6
325.2 + 4 15001 321.6
M
**
3298
1 3321
2
H
300;
600
I
3001
- 0 00
ALDES G . SHERWOOD HARRY E . GTJNSISG Fig. 2.-The
01
10
02 X
concentration dependence of t h e methyl resonances.
EDMONTON, ALBERTA,CANADA RECEIVED SEPTEMBER 12, 1963
symmetrical bidentate ligands have been detected by the splitting of the methyl resonance in the n.m.r. spectra. 2 , 3 With Zr(tfac)4, rapid ligand exchange makes Rapid Ligand Exchange in Zirconium(1V) Chelates all the methyl protons equivalent and no splitting is observed. Mixtures of Zr(acac), and Zr(tfac)4 have Sir : methyl resonances a t 320.0, 3 2 2 . 5 , 325.2, 337.6, 329.8, Several unsuccessful attempts to detect geometric or and 332.1 C.P.S. A typical spectrum is shown in Fig. 1. optical isomers of tetrakis-P-diketone complexes of In several of the spectra the resonances a t 323.2 and Zr(1V) and Hf(1V) suggest that in solution rapid 337.6 C.P.S. are asymmetric, indicating that two or more ligand exchange is occurring. This hypothesis has peaks are not being resolved. The concentration been verified by the n.ni.r. spectra of mixtures of dependence of the areas of the individual resonances is tetrakis- (2,4-pentanediono)-zirconium(IV) , Zr (acac),, and tetrakis-( I , l,l-trifluoro-2,-l-pentanediono)-zircon-shown in Fig. 2 . Here X represents the mole fraction of the acetylacetonate methyl groups and is equal iumiIV), Zr(tfac)4. to 2[acac] (2[acac] [tfac]),where [acac] and [tfac] Zr(acac), and Zr(tfac)? were prepared by a previously represent the total number of moles of acetylacetone reported method’ and were characterized by their and trifluoroacetylacetone, respectively. melting points and infrared spectra. The n.m.r. Because of rapid exchange of the ligands, a solution of spectra were obtained on a Varian Associates Model Zr(acac)l ?nd Zr(tfac)a contains the following five comA-60 spectrometer a t A 0 >IC. Samples were prepared pounds : Zr(acac)4, Zr (acac):
