Gyroscope-Like Platinum and Palladium Complexes with Trans-Spanning Bis(pyridine) Ligands

Pyridines with one or two substituents terminating in vinyl groups are prepared. Intramolecular ring-closing metatheses of trans -MCl 2 adducts and hydrogenations supply the title compounds. Williamson ether syntheses using the alcohols HO(CH 2 ) n CH═CH 2 ( n = 1 ( a ), 2 ( b ), 3 ( c ), 4 ( d ), 5 ( e ), 6 ( f ), 8 ( h ), 9 ( i )) and appropriate halides give the pyridines 2-NC 5 H 4 (CH 2 O(CH 2 ) n CH═CH 2 ) ( 1a, b ), 3-NC 5 H 4 (CH 2 O(CH 2 ) n CH═CH 2 ) ( 2a – e, h, i ), and 2,6-NC 5 H 3 (CH 2 O(CH 2 ) n CH═CH 2 ) 2 ( 4a – d ) in 92–45% yields. Reactions of 3,5-NC 5 H 3 (COCl) 2 and HO(CH 2 ) n CH═CH 2 afford the diesters 3,5-NC 5 H 3 (COO(CH 2 ) n CH═CH 2 ) 2 ( 5a – f, h, 90–41%). The reaction of 3,5-NC 5 H 3 (4-C 6 H 4 OH) 2, Br(CH 2 ) 5 CH═CH 2, and Cs 2 CO 3 yields 3,5-NC 5 H 3 (4-C 6 H 4 O(CH 2 ) 5 CH═CH 2 ) 2 ( 8; 32%). Reactions of PtCl 2 with 1a, b, 2a – e, h, i, 4a, b (but not 4c, d ), 5a, c – f, h, and 8 afford the corresponding bis(pyridine) complexes trans - 10a, b (40–12%), trans - 12a – e, h, i (84–46%), trans - 17a, b (88–22%), trans - 19a, c – f, h (94–63%), and trans - 22 (96%). Selected adducts are treated with Grubbs’ catalyst and then H 2 (Pd/C) to give trans - PtCl 2 [2,2′-(NC 5 H 4 (CH 2 O(CH 2 ) 2 n +2 OCH 2 )H 4 C 5 N)] ( trans - 11a, b; 79–63%), trans - PtCl 2 [3,3′-(NC 5 H 4 (CH 2 O(CH 2 ) 2 n +2 OCH 2 )H 4 C 5 N)] ( trans - 13, d, h, i; 93–80%), trans - PtCl 2 [2,6,2′,6′-(NC 5 H 3 (CH 2 O(CH 2 ) 2 n +2 OCH 2 ) 2 H 3 C 5 N)] ( trans - 18a, b; 22–10%), trans - PtCl 2 [3,5,3′,5′-(NC 5 H 3 (COO(CH 2 ) 2 n +2 OCO) 2 H 3 C 5 N)] ( trans- 20d – f, h; 45–14%), and trans - PtCl 2 [3,5,3′,5′-(NC 5 H 3 (4-C 6 H 4 O(CH 2 ) 12 O-4-C 6 H 4 ) 2 H 3 C 5 N)] (40%). A previously reported ring-closing metathesis of trans -PdCl 2 [2,6-NC 5 H 3 (CH 2 CH 2 CH═CH 2 ) 2 ] 2 is confirmed, and the new hydrogenation product trans - PdCl 2 [2,6,2′,6′-(NC 5 H 3 ((CH 2 ) 6 ) 2 H 3 C 5 N)] ( trans- 16; 62%) is isolated. Additions of CH 3 MgBr to 12b, h and 13d, h afford the corresponding PtClCH 3 species (94–41%), but analogous reactions fail with 2-substituted pyridine adducts. The reaction of trans - 19c with PhC≡CH and CuI/ i -Pr 2 NH gives the corresponding PtCl(C≡CPh) adduct (18%). The crystal structures of trans - 17a, trans - 11b, trans - 13d, trans - 13h ·CH 2 Cl 2, trans - 16, trans - 18a, b, and trans - 20e ·2CHCl 3 are determined. Steric effects in the preceding data, especially involving 2-substituents and the MCl 2 or MCl(X) rotators, are analyzed in detail.