No abstract

2,2,3-Triphenyl-ZH-azirine (4a) in a matrix of 2,2-dimethylbutane/pentane 8 : 3(DMBP) at -185' gave rise on irradiation with light of 250-350 nm to a new UV.-maximum at 350 nm (Fig. 1). We assign the dipole benzonitrildiphenylmethylide (la) to this new maximum. Irradiation with monochromatic light of 366 nm destroyed this maximum and the initial absorption curve reappeared (Fig. 2). When the azirine 4a was photolysed in DMBP at -185" in the presence of methyl trifluoracetate (TFEM), the maximum at 350 nm was obtained again. This maximum vanished upon increasing the temperature to -160". Through gas chromatography we were able to show that 5-methoxy-5-trifluormethyl-2,2,4-triphenyl-3-oxazoline (6a) was produced. 6a was also obtained upon irradiation of 4a a t room temperature in the presence of TFEM (scheme 1 and table 1). Modification of the previously described experiment, in which the maximum a t 350 nm was extinguished in the matrix due to irradiation at 366 nm gave, after warm up, almost no dipole adduct 6a (table 1). From these experiments, an extinction coefficient of 17,000 for the 350 nm maximum of la, was calculated. These experiments have shown that irradiation of triphenylazirine 4a leads to the dipole la, which can be reversed photochemicallybut not thermallyinto azirine 4a. l a reacts a t less than -160" with TFEM to give adduct 6a. The results which were obtained with triphenylazirine 4a could be correspondingly obtained with 2,J-diphenyl-2H-azirine 4b (Fig. 3, scheme 2 and table 2 ) . The dipole l b showed two UV.maxima at 330 nm (e = 17,500) and 343 nm (E = 21,000). Later experiments established. that the two maxima belonged to a single dipole species.The dipole lc obtained upon irradiation of 2,2-dirnethyl-3-phenyl-ZH-azirine (4c) in DMBP at -190°, appears to absorb in the same region as the azirinc 4c. The presence of the dipole lc was univocally established by low temperature trapping experiments with TFEM. The dipole l a showed no ESR.-spectrum characteristic for a triplet state. We assume therefore, that la is in a singlet state. Photolysis of oxazolinone 7 at -190" in DMBP led to the dipole l a with loss of CO,. la recombines apparently in considerable amount with the CO, trapped in the matrix to l ) %) 27. Mitt. iiber Photoreaktionen; 26. Mitt. [l] ; 25. Mitt. [Z].

Crystallographic Procedures. Crystalline samples suitable for diffraction analysis were obtained as follows. Colorless crystals of 1 were obtained from benzene solution at room temperature. Light-yellow crystals of 2 were obtained from the reaction mixture in benzene at 5 °C. Colorless crystals of 3 and dark-red crystals of 5 were obtained from the respective reaction mixtures at -20 eC. Dark-purple plates of 6-THF were obtained from the reaction mixture in hexane at room temperature.All samples were mounted in thin-wall glass capillaries in an inertatmosphere glovebox. The intensity data for compounds 1, 3, and 5 were collected on a Siemens R3m/v diffractometer at ambient temperature. The data for 2 and 6 were collected on a Nicolet P3 diffractometer at ambient temperature. On both diffractometers, Mo Ka radiation (X = 0.71073 A) was used except in the case of 1 for which Cu Ka radiation was used (X = 1.541 78 A).Crystallographic calculations were done on a microVAX II using the Siemens SHELXTL PLUS program package. Crystal data are summarized in Table II. Neutral-atom scattering factors were used.55 All structures were solved by direct methods. On the basis of systematic extinctions or lack of them, the space groups were assigned to be PI (No.2) for 1-3, and 6, and P2,2I2, (No. 19) for 5. Refinements for each are described in the supplementary material. All non-hydrogen atoms were refined anisotropically. All hydrogen atoms were placed in calculated (55) International Tables for X-ray Crystallography; Hahn, T., Ed.

~~~~~ The preparation of complexes [MX,(I)] (M = Ni, Pd, and Pt; X = C1, Br, and 1; 1 = 1,2-bis[(diphenylphosphino)niethyl]benzene), [Pt(OSO,CH,)Et(l)], [Pt(alkene)(l)] (alkene = C,H, and CH2 = CHCN), and [(l)Pt-(p-H),PtH(l)][BPh,] is reported.Their 'H-and 3'P-NMR spectra were recorded and used for structural assignments. The X-ray crystal structure of [Pt(C,H,)(l)] was determined. It is shown that the P-Pt-P bond angle in this complex differs significantly from those found in related compounds with monodentate phosphines, and that this difference is likely to be due to intramolecular contacts.