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-MCl2 adducts and hydrogenations supply the title compounds.
Williamson ether syntheses using the alcohols HO­(CH2)nCHCH2 (n = 1 (a), 2 (b), 3 (c), 4
(d), 5 (e), 6 (f), 8 (h), 9 (i)) and appropriate halides give the pyridines
2-NC5H4(CH2O­(CH2)nCHCH2) (1a,b), 3-NC5H4(CH2O­(CH2)nCHCH2) (2a–e,h,i), and
2,6-NC5H3(CH2O­(CH2)nCHCH2)2 (4a–d) in 92–45% yields. Reactions
of 3,5-NC5H3(COCl)2 and HO­(CH2)nCHCH2 afford
the diesters 3,5-NC5H3(COO­(CH2)nCHCH2)2 (5a–f,h, 90–41%). The
reaction of 3,5-NC5H3(4-C6H4OH)2, Br­(CH2)5CHCH2, and Cs2CO3 yields 3,5-NC5H3(4-C6H4O­(CH2)5CHCH2)2 (8; 32%). Reactions
of PtCl2 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 H2 (Pd/C) to give trans-PtCl2[2,2′-(NC5H4(CH2O­(CH2)2n+2OCH2)­H4C5N)] (trans-11a,b; 79–63%), trans-PtCl2[3,3′-(NC5H4(CH2O­(CH2)2n+2OCH2)­H4C5N)] (trans-13,d,h,i; 93–80%), trans-PtCl2[2,6,2′,6′-(NC5H3(CH2O­(CH2)2n+2OCH2)2H3C5N)] (trans-18a,b; 22–10%), trans-PtCl2[3,5,3′,5′-(NC5H3(COO­(CH2)2n+2OCO)2H3C5N)] (trans-20d–f,h; 45–14%),
and trans-PtCl2[3,5,3′,5′-(NC5H3(4-C6H4O­(CH2)12O-4-C6H4)2H3C5N)] (40%). A previously reported
ring-closing metathesis of trans-PdCl2[2,6-NC5H3(CH2CH2CHCH2)2]2 is confirmed, and the new hydrogenation
product trans-PdCl2[2,6,2′,6′-(NC5H3((CH2)6)2H3C5N)] (trans-16; 62%) is isolated. Additions of CH3MgBr
to 12b,h and 13d,h afford the corresponding PtClCH3 species (94–41%),
but analogous reactions fail with 2-substituted pyridine adducts.
The reaction of trans-19c with PhCCH
and CuI/i-Pr2NH gives the corresponding
PtCl­(CCPh) adduct (18%). The crystal structures of trans-17a, trans-11b, trans-13d, trans-13h·CH2Cl2, trans-16, trans-18a,b, and trans-20e·2CHCl3 are determined. Steric effects in the preceding
data, especially involving 2-substituents and the MCl2 or
MCl­(X) rotators, are analyzed in detail.