Three-Fold Intramolecular Ring Closing Alkene Metatheses of Square Planar Complexes with <i>cis</i> Phosphorus Donor Ligands P(X(CH₂)_<i>m</i>CHCH₂)₃ (X = −, <i>m</i> = 5–10; X = O, <i>m</i> = 3–5): Syntheses, Structures, and Thermal Properties of Macrocyclic Dibridgehead Diphosphorus Complexes

Reactions of cis-PtCl2(P­((CH2)mCHCH2)3)2 and Grubbs’ first generation catalyst and then hydrogenations afford cis-PtCl2(P­((CH2)n)3P) (cis-2; n = 2m + 2 = 12 (b), 14 (c), 16 (d), 18 (e), 20 (f), 22 (g); 6–40%), derived from 3-fold interligand metatheses. The phosphite complexes cis-PtCl2(P­(O­(CH2)m*CHCH2)3)2 are similarly converted to cis-PtCl2(P­(O­(CH2)n*O)3P) (cis-5; n* = 8 (a), 10 (b), 12 (c), 10–20%). The substitution products cis-PtPh2(P­((CH2)n)3P) (cis-6c,d) and cis-PtI2(P­(O­(CH2)10O)3P) are prepared using Ph2Zn and NaI, respectively. Crystal structures of cis-2c,d,f, cis-5a,b, and cis-6c show one methylene bridge that roughly lies in the platinum coordination plane and two that are perpendicular. The thermal behavior of the complexes is examined. When the bridges are sufficiently long, they rapidly exchange via an unusual “triple jump rope” motion over the PtX2 moieties. NMR data establish ΔH⧧, ΔS⧧, and ΔG298K⧧/ΔG393K⧧ values of 7.8 kcal/mol, −27.9 eu, and 16.1/18.8 kcal/mol for cis-2d, and a ΔG393K⧧ of ≥19.6 kcal/mol for the shorter bridged cis-2c. While cis-2c,g gradually convert to trans-2c,g at 150–185 °C in haloarenes, trans-2c,g give little reaction under analogous conditions, establishing the stability order trans > cis. Similar metathesis/hydrogenation sequences with octahedral complexes containing two cis phosphine ligands, fac-ReX­(CO)3(P­((CH2)6CHCH2)3)2 (X = Cl, Br), give fac-ReX­(CO)3(P­(CH2)13CH2)­((CH2)14)­(P­(CH2)13CH2) (19–50%), which are derived from a combination of interligand and intraligand metathesis. The relative stabilities of cis/trans and other types of isomers are probed by combinations of molecular dynamics and DFT calculations.