Gyroscope-like molecules consisting of PdX/PtX rotators within three-spoke dibridgehead diphosphine stators: syntheses, substitution reactions, structures, and dynamic properties.
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abstract
Threefold intramolecular ring-closing metatheses of trans-[MCl2(P{(CH2)(m)CH=CH2}3)2] are effected with Grubbs' catalyst. Following hydrogenation catalyzed by [RhCl(PPh3)3], the title complexes trans-[MCl2(P((CH2)n)3P)] (n=2m+2; M/n=Pt/14, 4c; Pt/16, 4d; Pt/18, 4e; Pd/14, 5c; Pd/18, 5e) and sometimes isomers partly derived from intraligand metathesis, trans-[MCl2{P(CH2)n(CH2)n}P(CH2)n)] (4'c-e, 5'e), are isolated. These react with LiBr, NaI, and KCN to give the corresponding MBr2, MI2, and M(CN)2 species (58-99%). (13)CNMR data show that the MX2 moieties rapidly rotate within the diphosphine cage on the NMR timescale, even at -120C. The reaction of 4c and KSCN gives separable Pt(NCS)2 and Pt(NCS)(SCN) adducts (13c, 28%; 14c, 20%), and those of 4c,e and Ph2Zn give PtPh2 species (15c, 61%; 15e, 90%). (13)CNMR spectra of 13c-15c show twosets of CH2 signals (ca. 2:1 intensity ratios), indicating that MX2 rotation is no longer rapid. Reactions of 4c or 4'c and excess NaCCH afford the free diphosphines P{(CH2)14}3P (91%) and (CH2)14P(CH2)14P(CH2)14 (90%). The latter has been crystallographically characterized as a bis(BH3) adduct. The crystal structures of eight complexes with P(CH2)14P linkages (PtCl2, PtBr2, PtI2, Pt(NCS)2, PtPh2, PdCl2, PdBr2, PdI2) and 15e have been determined, and intramolecular distances analyzed with respect to MX2 rotation. The conformations of the (CH2)14 moieties and features of the crystal lattices are also discussed.
