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Dalton Transactions

The international journal for inorganic, organometallic and bioinorganic chemistry



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Dalton Trans., 2004, 1012 - 1028, DOI: 10.1039/b400156g

Alkene metatheses in transition metal coordination spheres: dimacrocyclizations that join trans positions of square-planar platinum complexes to give topologically novel diphosphine ligands

Takanori Shima, Eike B. Bauer, Frank Hampel and J. A. Gladysz

The alkene-containing phosphines PPh((CH2)nCHCH2)2)2( 4) are prepared from PPhH2, n-BuLi, and the corresponding bromoalkenes (1 2 2), and combined with the platinum tetrahydrothiophene complex [Pt(µ-Cl)(C6F5)(S(CH2CH2–)2)]2( 12) to give the square-planar adducts trans-(Cl)(C6F5)Pt(PPh((CH2)nCHCH2)2)2( 11, 93–73%; n=a, 2; b, 3; c, 4; d, 5; e, 6; f, 8). Ring-closing metatheses with Grubbs' catalyst ( 2) are studied. With 11e, two isomers of trans-(Cl)(C6F5)Pt(PPh(CH2)14P(CH2)14Ph)( 15e) are isolated after hydrogenation. Both form via dimacrocyclization between the trans-phosphine ligands, but differ in the dispositions of the PPh rings (syn, 31%; anti, 7%). The alternative intraligand metathesis product trans-(Cl)(C6F5)Pt(PPh(CH2)14)2( 16e) is independently prepared by (i) protecting 4e as a borane adduct, H3B·PPh((CH2)6CHCH2)2, (ii) cyclization with 2 and hydrogenation to give H3B·PPh(CH2)14, (iii) deprotection and reaction with 12. The sample derived from 11e contains 2% 16e; mass spectra suggest that the other products are dimers or oligomers. The structures of syn- 15e, anti- 15e and 16e are verified crystallographically, and the macrocycle conformations analyzed. As expected from the (CH2)n segment length, 11a undergoes intraligand metathesis to give (Z,Z)-trans-(Cl)(C6F5)Pt(PPh(CH2)2CHCH(CH2)2)2(86%), as confirmed by a crystal structure of the hydrogenation product. Although 11b does not yield tractable products, 11c gives syn-(E,E)-trans-(Cl)(C6F5)Pt(PPh(CH2)4CHCH(CH2)4P(CH2)4CHCH(CH2)4Ph)(21%). This structure, and that of the hydrogenation product (syn- 15c; 95%), are verified crystallographically. Analogous sequences with 11d,f give syn- 15d,f(5 and 14% overall).

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