Calix[4]arene Ligands with Phosphorus-Containing Groups Tethered at the Upper Rim

The preparation and coordinative properties of two upper-rim functionalized calixarenes, 5,17-bis(tert-butyl)-11,23-bis(diethoxyphosphinomethoxy)-25,26,27,28-tetrakis(2-ethoxyethoxy)calix [4] arene (4) and 5,17-bis(tert-butyl)-11,23-bis(diphenylphosphinomethyl)-25,26,27,28-tetrakis(2-ethoxyethoxy)calix[4]arene (6) are presented.
Diphosphine 6 was oxidized by air to the corresponding di(phosphine oxide) 7. The molecular structure of 7·2CHCl3 was elucidated by X-ray crystallography:  C78H94O10P2·2CHCl3, a = 16.313 (5) Å, b = 16.553(5) Å, c
= 17.068(6) Å, α = 108.04(2)°, β = 93.13(2)°, γ = 100.27(2)°, Z = 2. The calixarene matrix displays a pinched
cone conformation, with the two tBu-phenoxy rings of the macrocycle lying almost perpendicular (interplanar
angle 84.7°) and the other two phenoxy rings making an angle of 20.9°. Reaction of 6 with 2 equiv of [AuCl(SC4H8)] (SC4H8 = tetrahydrothiophene) in CH2Cl2 afforded the digold complex 6·(AuCl)2 (8). Reaction of 6
with [RuCl2(p-cymene)]2 resulted in formation of the dinuclear complex 6·[RuCl2(p-cymene)]2 (9) while the rhodium
complex 6·[RhCl(norbornadiene)]2 (10) was formed by reaction of 6 with [RhCl(norbornadiene)]2. Complex 10
catalyzes hydroformylation of styrene (CO/H2 = 1, P = 40 bar, 70 °C, styrene/Rh ∼ 585) in the presence of
NEt3, from which linear and branched aldehydes were obtained in a 9:91 ratio. Diphosphite 4 was found to be
suitable for chelate formation; thus [Pd(η3-MeC3H4)(thf)2]BF4 (thf = tetrahydrofuran) reacts with 4 to yield the
mononuclear complex [4·{Pd(η3-MeC3H4)}]BF4 (11), where the metal is located at the mouth of the cavity. All
complexes were characterized by elemental analyses and by 1H, 13C, and 31P NMR spectroscopy.