Protonation of Zwitter-Ionic Manganese and Rhenium Phosphoniostyryl Complexes (I·5-C5H5)(CO) 2M--C(+PR3)=C(H)Ph: Experimental and DFT Studyстатья
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Аннотация:Stereoselective addition of tertiary phosphanes to manganese and rhenium phenylvinylidenes (I·5-C5H5)(CO) 2M=C=C(H)Ph (1 M = Mn; 2 M = Re) gave the corresponding zwitterionic Z-phosphoniostyryl adducts (I·5-C5H 5)(CO)2M--C(+PR3)=C(H)Ph (3 M = Mn, PR3 = PPh2Me; 4 Mn, PPhMe2; 5 Mn, PMe3; 6 Re, PPh2Me; 7 Re, PMe3). Protonation of 3-7 with HBF4·OEt2 resulted in the formation of the I·2-phosponioalkene complexes (I·5- C5H5)(CO)2M(I·2-E-HC( +PR3)=C(H)Ph) (8 Mn, PPh2Me; 9 Mn, PPhMe 2; 10 Mn, PMe3; 11 Re, PPh2Me; 12 Re, PMe 3) rather than in the corresponding phosphoniocarbene complexes (I·5-C5H5)(CO)2M=C( +PR3)CH2Ph. It was shown by DFT calculations (B3LYP/6-31G*) that the protonation of 5 proceeds at the metal atom followed by C,H-reductive elimination in the intermediate hydride cis-(I·5-C5H5)(CO)2(H)Mn- C(+PMe3)=C(H)Ph (14) to form the agostic complex (I·5-C5H5)(CO)2Mn{I· 2-H-C(+PMe3)=C(H)Ph} (15) and subsequent isomerization of the latter into the final I·2- phosphonioalkene 10. In line with the theoretical data, the low-temperature protonation (-80°C) of 3 with triflic acid in an NMR tube directly gave the corresponding phosponioalkene complex 8. Unlike 3, the protonation of their rhenium analogues 6 and 7 under the same conditions revealed the quantitative formation of cis-hydride intermediates cis-[(I·5-C 5H5)(CO)2(H)Re-C(+PR 3)=C(H)Ph]OTf (16, 17), which undergo conversion into the corresponding I·2-phosponioalkene complexes 11 and 12 at ca. -30°C Protonation of Mn and Re Z-σ-phosphoniostyryl complexes 3-7 with HBF4·OEt2 leads to the E-I·2- phosphonioalkene derivatives 8-12 rather than the phosphoniocarbene complexes 13. According to DFT calculations, protonation of Mn complex 5 proceeds at the metal atom followed by fast conversion of the resulting cis-hydride 14 into the agostic intermediate 15 and the final product 10. Quantitative formation of the cis-hydride intermediates 16 and 17 was evidenced by low-temperature protonation of the rhenium Z-σ-phosphoniostyryl complexes 6 and 7 with triflic acid.