Alkene metatheses in transition metal coordination spheres: dimacrocyclizations that join trans positions of square-planar platinum complexes to give topologically novel diphosphine ligands
Abstract
The alkene-containing CH2)2)2
(4) are prepared from PPhH2, n-BuLi, and the corresponding
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)14P
(C
H2)14Ph)
(15e) are isolated after hydrogenation. Both form via dimacrocyclization between the trans-phosphine
PPh(C
H2)14)2
(16e) is independently prepared by (i) protecting 4e as a borane adduct, H3B·PPh((CH2)6CH
CH2)2, (ii) cyclization with 2 and hydrogenation to give H3B·
PPh(C
H2)14, (iii) deprotection and reaction with 12. The sample derived from 11e contains ≤2%
16e;
PPh(CH2)2CH
CH(C
H2)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)4CH
CH(CH2)4P
(CH2)4CH
CH(C
H2)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).