Building Blocks for Molecular Polygons Based on Platinum Vertices and Polyynediyl Edges.

Reactions of Cl2P(CH2)3PCl2 and p-MgBrC6H4X (X = a/OMe, b/OtBu, c/tBu, d/SiMe3) give the diphosphines (p-XC6H4)2P(CH2)3P(p-C6H4X)2 (1a-d; 47-66%). Additions of 1a,d to (COD)PtCl2 yield (CH2(CH2P(p-C6H4X)2)2)PtCl2 (2a,d; 62-88%), which upon reaction with butadiyne (2 equiv; HNEt2/cat. CuI) give (CH2(CH2P(p-C6H4X)2)2)Pt((C≡C)2H)2 (3a,d; 34-76%). Alternatively, 3a-d can be accessed from trans-(p-tol3P)2Pt((C≡C)2H)2 and 1a-d (30-87%). Reactions of (p-tol3P)2PtCl2 and H(C≡C)2SiR3 (2 equiv, HNEt2/cat. CuI; R = Me/Et/iPr) give trans-(p-tol3P)2Pt((C≡C)2SiR3)2 (77-95%), and subsequent additions of 1a,b,d yield the corresponding adducts (CH2(CH2P(p-C6H4X)2)2)Pt((C≡C)2SiR3)2 (R/X = Me/OMe, 5a; iPr/OMe, 6a; iPr/OtBu, 6b; iPr/SiMe3, 6d; 52-95%) and (for 5a) a luminescent diplatinum byproduct with trans Pt((C≡C)2SiMe3)2 units. 5a and 6b hydrolyze in the presence of F- to 3a,b (92-93%). Reaction of 2a and 3a (HNEt2/cat. CuI) affords the Pt4C16 polygon ([(CH2(CH2P(p-C6H4OMe)2)2)Pt(C≡C)2]4 as an H2NEt2+ Cl- adduct (66%). The 13C{1H} NMR spectra of 3a-d, 5a, and 6a,b,d feature complex AMXX' (CPtPP') spin systems, and simulations allow J values to be extracted. The crystal structures of 2a, 3a,b,d, 5a, and 6a are determined and analyzed.

Monodisperse Molecular Models for the sp Carbon Allotrope Carbyne; Syntheses, Structures, and Properties of Diplatinum Polyynediyl Complexes with PtC20Pt to PtC52Pt Linkages.

Extended conjugated polyynes provide models for the elusive sp carbon polymer carbyne, but progress has been hampered by numerous synthetic challenges. Stabilities appear to be enhanced by bulky, electropositive transition-metal endgroups. Reactions of trans-(C6F5)(p-tol3P)2Pt(C≡C)nSiEt3 (n = 4-6, PtCxSi (x = 2n)) with n-Bu4N+F-/Me3SiCl followed by excess tetrayne H(C≡C)4SiEt3 (HC8Si) and then CuCl/TMEDA and O2 give the heterocoupling products PtCx+8Si, PtCx+16Si, and sometimes higher homologues. The PtCx+16Si species presumably arise via protodesilylation of PtCx+8Si under the reaction conditions. Chromatography allows the separation of PtC16Si, PtC24Si, and PtC32Si (from n = 4), PtC18Si and PtC26Si (n = 5), or PtC20Si and PtC28Si (n = 6). These and previously reported species are applied in similar oxidative homocouplings, affording the family of diplatinum polyynediyl complexes PtCxPt (x = 20, 24, 28, 32, 36, 40 in 96-34% yields and x = 44, 48, 52 in 22-7% yields). These are carefully characterized by 13C NMR, UV-visible, and Raman spectroscopy and other techniques, with particular attention to behavior as the Cx chain approaches the macromolecular limit and endgroup effects diminish. The crystal structures of solvates of PtC20Pt, PtC24Pt, and PtC26Si, which feature the longest sp chains structurally characterized to date, are analyzed in detail. All data support a polyyne electronic structure with a nonzero optical band gap and bond length alternation for carbyne.

Trapping of Terminal Platinapolyynes by Copper(I) Catalyzed Click Cycloadditions; Probes of Labile Intermediates in Syntheses of Complexes with Extended sp Carbon Chains, and Crystallographic Studies.

The silylated hexatriynyl complex trans-(C6 F5 )(p-tol3 P)2 Pt(C≡C)3 SiEt3 (PtC6 TES) is converted in situ to PtC6 H (wet n-Bu4 N+ F- , THF) and cross coupled with the diyne H(C≡C)2 SiEt3 (HC4 TES; CuCl/TMEDA, O2 ) to give PtC10 TES (71 %). This sequence is repeated twice to afford PtC14 TES (65 %) and then PtC18 TES (27 %). An analogous series of reactions starting with PtC8 TES gives PtC12 TES (60 %), then PtC16 TES (43 %), and then PtC20 TES (17 %). Similar cross couplings with H(C≡C)2 Si(i-Pr)3 (HC4 TIPS) give PtC12 TIPS (68 %), PtC14 TIPS (68 %), and PtC16 TIPS (34 %). The trialkylsilyl species (up to PtC18 TES) are converted to 3+2 "click" cycloadducts or 1,4-disubstituted 1,2,3-triazoles trans-(C6 F5 )(p-tol3 P)2 Pt(C≡C)n-1 C=CHN(CH2 C6 H5 )N=N (29-92 % after workups). The most general procedure involves generating the terminal polyynes PtCx H (wet n-Bu4 N+ F- , THF) in the presence of benzyl azide in DMF and aqueous CuSO4 /ascorbic acid. All of the preceding complexes are crystallographically characterized and the structural and spectroscopic properties analyzed as a function of chain length. Two pseudopolymorphs of PtC20 TES are obtained, both of which feature molecules with parallel sp carbon chains in a pairwise head/tail packing motif with extensive sp/sp van der Waals contacts.

Syntheses, Structures, and Spectroscopic Properties of 1,10-Phenanthroline-Based Macrocycles Threaded by PtC8 Pt, PtC12 Pt, and PtC16 Pt Axles: Metal-Capped Rotaxanes as Insulated Molecular Wires.

The platinum polyynyl complexes trans-(C6 F5 )(p-tol3 P)2 Pt(C≡C)n/2 H undergo oxidative homocoupling (O2 , CuCl/TMEDA) to diplatinum polyynediyl complexes trans, trans-(C6 F5 )(p-tol3 P)2 Pt(C≡C)n Pt(Pp-tol3 )2 (C6 F5 ) (n=4, 2; 6, 5; 8, 8; 92-97 %) as reported previously. When related reactions are conducted in the presence of CuI adducts of the 1,10-phenanthroline-based macrocycles 2,9-(1,10-phenanthrolinediyl)(p-C6 H4 O(CH2 )6 O)2 (1,3-C6 H4 ) (10, 33-membered) or 2,9-(1,10-phenanthrolinediyl)(p-C6 H4 O(CH2 )6 O)2 (2,7-naphthalenediyl) (11, 35-membered), excess K2 CO3 , and I2 (oxidant), rotaxanes are isolated that feature a Pt(C≡C)n Pt axle that has been threaded through the macrocycle (2⋅10, 9 %; 5⋅10, 41 %; 5⋅11, 28 %; 8⋅10, 12 %; 8⋅11, 9 %). Their crystal structures are determined and analyzed in detail, particularly with respect to geometric perturbations and the degree of steric sp carbon chain insulation. NMR spectra show a number of shielding effects. UV/Vis spectra do not indicate significant electronic interactions between the Pt(C≡C)n Pt axles and macrocycles, although cyclic voltammetry data suggest rapid reactions following oxidation.

Photophysics of platinum tetrayne oligomers: delocalization of triplet exciton.

A series of platinum tetrayne oligomers, all-trans-Cl-Pt(P2)-[(C≡C)4-Pt(P2)]n-Cl, where P = tri(p-tolyl)phosphine and n = 1-3, was subjected to a detailed photophysical investigation. The photoluminescence of each oligomer at low temperature (T < 140 K) in a 2-methyltetrahydrofuran (Me-THF) glass features an intense and narrow 0-0 phosphorescence band accompanied by a vibronic progression of sub-bands separated by ca. 2100 cm(-1). The emission arises from a (3)π,π* triplet state concentrated on the (C≡C)4 carbon chain and the vibronic progression originates from coupling of the excitation to the ν(C≡C) stretch. All of the experimental data including ambient temperature absorption, low-temperature photoluminescence, and ambient temperature transient absorption spectroscopy provide clear evidence that the triplet state is localized on a chromophore consisting of approximately two -[(C≡C)4-Pt(P2)]- repeat units. Density functional theory calculations support the hypothesis that the triplet-triplet absorption arises from transitions that are delocalized over two repeat units.

A new type of insulated molecular wire: a rotaxane derived from a metal-capped conjugated tetrayne.

The platinum butadiynyl complex trans-(C(6)F(5))(p-tol(3)P)(2)Pt(C≡C)(2)H and a CuI adduct of a 1,10-phenanthroline based 33-membered macrocycle react in the presence of K(2)CO(3) and I(2) or O(2) to give a rotaxane (ca. 9%) in which the macrocycle is threaded by the sp carbon chain of trans,trans-(C(6)F(5))(p-tol(3)P)(2)Pt(C≡C)(4)Pt(Pp-tol(3))(2)(C(6)F(5)). The crystal structure and macrocycle/axle electronic interactions are analyzed in detail.

Towards multistranded molecular wires: syntheses, structures, and reactivities of tetraplatinum bis(polyynediyl) complexes with [upper bond 1 start]Pt-C(x)-Pt-(P(CH2)3P)2-Pt-C(x)-Pt-(P(CH2)3P[upper bond 1 end])2 cores (x = 4, 6, 8).

Reactions of trans,trans-(C(6)F(5))(p-tol(3)P)(2)Pt(C[triple bond]C)(n)Pt(Pp-tol(3))(2)(C(6)F(5)) (PtC(x)Pt; x = 2n) and the 1,3-diphosphine Ph(2)P(CH(2))(3)PPh(2) (2.5 equiv) give the tetraplatinum complexes trans, trans,trans,trans-(C(6)F(5))[upper bond 1 start]Pt(C[triple bond]C)(n)Pt(C(6)F(5))(PPh(2)(CH(2))(3)Ph(2)P)(2)(C(6)F(5))Pt(C[triple bond]C)(n)Pt(C(6)F(5))(PPh(2)(CH(2))(3)Ph(2)P[upper bond 1 end])(2) ([Pt'C(x)Pt'](2); x = 4/6/8, 39%/95%/81%). Crystal structures of [Pt'C(8)Pt'](2) and two solvates of [Pt'C(6)Pt'](2) are determined. These confirm that each diphosphine spans two platinum atoms from different Pt(C[triple bond]C)(n)Pt linkages, as opposed to (1) the 1,2-diphosphine Ph(2)P(CH(2))(2)PPh(2), which under similar conditions with PtC(8)Pt affords the diplatinum bis(chelate) cis,cis-([upper bond 1 start]PPh(2)(CH(2))(2)Ph(2)P)(C(6)F(5))Pt[upper bond 1 end](C[triple bond]C)(4)[upper bond 1 start]Pt(C(6)F(5))(PPh(2)(CH(2))(2)Ph(2)P[upper bond 1 end]) (73%) or (2) alpha,omega-diphosphines with longer methylene chains, which span the platinum termini. The formulation [Pt'C(4)Pt'](2) is supported by a reaction with PEt(3) (10 equiv) to give trans,trans-(C(6)F(5))(Et(3)P)(2)Pt(C[triple bond]C)(2)Pt(PEt(3))(2)(C(6)F(5)). In [Pt'C(8)Pt'](2) and one solvate of [Pt'C(6)Pt'](2), the chains cross at 77.2 degrees-87.7 degrees angles, with the closest interchain carbon-carbon distances (3.27-3.61 A) less than the sum of the van-der-Waals radii. In the other solvate of [Pt'C(6)Pt'](2), the chains are essentially parallel, and the separation is much greater (4.96 A). UV-visible spectra show no special electronic interactions. However, cyclic voltammograms indicate irreversible oxidations, in contrast to the partially reversible oxidations of PtC(6)Pt and PtC(8)Pt. The initially formed radical cations are proposed to undergo rapid chain-chain coupling. The new complexes decompose without melting above 185 degrees C. With [Pt'C(8)Pt'](2), IR spectra indicate the formation of a new C[triple bond]C-rich substance.