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

The alkene-containing phosphines PPh((CH2)(n)CH = CH2)(2))(2) (4) are prepared from PPhH2, n-BuLi, and the corresponding bromoalkenes (1 : 2 : 2), and combined with the platinum tetrahydrothiophene complex [Pt(mu-Cl)(C6F5)(S(CH2CH2-)(2))](2) (12) to give the square-planar adducts trans-(Cl)(C6F5) Pt(PPh((CH2)(n)CH = CH2)(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)(14)P(CH2)(14)Ph) (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)(6)CH = CH2)(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 less than or equal to2% 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)(2)CH=CH(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)(4)CH=CH(CH2)(4)P(CH2)(4)CH = CH(CH2)(4)Ph) (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).