C8 and C12 sp Carbon Chains That Span Two Platinum Atoms: The First Structurally Characterized 1,3,5,7,9,11-Hexayne

Article abstract of DOI:10.1021/om990448c

Reaction sequences involving trans-(p-tol)-(Ar₃P)₂PtCl (Ar = Ph, p-tol), HC≡CC≡CH, HC≡CSiEt₃, and oxidative ≡CH/HC≡ cross- or homocoupling (O₂, cat. CuCl/TMEDA) give the C_x complexes trans,trans-(p-to

Full text of DOI:10.1021/om990448c

Organometallics 1999, 18, 3261-3263
3261
C8 a n d C12 sp Ca r bon Ch a in s Th a t Sp a n Tw o P la tin u m
Atom s: Th e F ir st Str u ctu r a lly Ch a r a cter ized
1,3,5,7,9,11-Hexa yn e
Thomas B. Peters,† J ames C. Bohling,† Atta M. Arif,† and J . A. Gladysz*,†,‡,§
Department of Chemistry, University of Utah, Salt Lake City, Utah 84112, and Institut fu¨r
Organische Chemie, Friedrich-Alexander Universita¨t Erlangen-Nu¨rnberg, Henkestrasse 42,
91054 Erlangen, Germany
Received J une 10, 1999
Summary: Reaction sequences involving trans-(p-tol)-
(Ar3P)2PtCl (Ar ) Ph, p-tol), HCtCCtCH, HCtCSiEt3,
and oxidative tCH/ HCt cross- or homocoupling (O2,
cat. CuCl/ TMEDA) give the Cx complexes trans,trans-
(p-tol)(Ar3P)2Pt(CtC)nPt(PAr3)2(p-tol) (n ) 4, 6), which
have been characterized by crystallography and by IR,
NMR, and UV-visible spectroscopy.
many challenges. For example, the possibility that
carbyne might easily bend and generate other allotropes
has received considerable speculation,6 but experimental
probes remain scant.
Several metal-capped octatetraynediyl systems LnMCt
CCtCCtCCtCMLn are now known.3 However, higher
C10-C20 homologues have so far only been accessed with
the chiral rhenium end group (η5-C5Me5)Re(NO)(PPh3).2e
These dirhenium compounds have yielded much valu-
able data. Nonetheless, the meso and dl diastereomers
are often inseparable, complicating some analyses.
Hence, we sought to develop parallel chemistry with
achiral end groups. In this communication, we report
that bis(phosphine)arylplatinum termini can also sup-
port C8-C12 chains, as well as crystal structures of C8
and C12 systems. The latter represents the longest
polyyne structurally characterized to date.7
Over the past few years, there has been rapidly
increasing interest in compounds where sp carbon
chains span two metal atoms,1-3 as well as sp carbon
rich organic systems.4,5 One important objective involves
methodology for the construction of longer sp carbon
chains. Such species constitute models for the polymeric
sp carbon allotrope “carbyne”,6 the precise physical and
chemical characterization of which continues to present
* Address correspondence to this author at the new Erlangen
permanent address.
We first prepared the building block (p-tol)(COD)PtCl
(1),8 which features (1) easily displaced diene and
chloride ligands and (2) a p-tol group to facilitate NMR
analyses. Reaction of 1 and p-tol3P (2.4 equiv) gave the
new bis(phosphine) complex trans-(p-tol)(p-tol3P)2PtCl
(2) in 94% yield after workup.9 As with all other
complexes below, 2 showed a single set of phosphine
NMR signals and virtual coupling patterns10 typical of
square-planar trans-bis(phosphine) complexes. As de-
picted in Scheme 1, a HNEt2 solution of 2 and CuI (0.12
equiv) was treated with excess HCtCCtCH11a in THF.
Workup gave the 1,3-butadiynyl complex trans-(p-tol)-
(p-tol3P)2PtCtCCtCH (3) as a tan powder in 79%
† University of Utah.
‡ Friedrich-Alexander Universita¨t Erlangen-Nu¨rnberg.
§ This paper is dedicated to a pioneer in this field and a neighbor in
Franconia, Prof. Dr. Helmut Werner, on the occasion of his 65th
birthday.
(1) (a) Bruce, M. I. Coord. Chem. Rev. 1997, 166, 91. (b) Paul, F.;
Lapinte, C. Coord. Chem. Rev. 1998, 178-180, 427. (c) Apropos the
dedication, see: Gevert, O.; Wolf, J .; Werner, H. Organometallics 1996,
15, 2806. Werner, H. J . Chem. Soc., Chem. Commun. 1997, 903
(review).
(2) Full papers from our laboratory: (a) Weng, W.; Bartik, T.; Brady,
M.; Bartik, B.; Ramsden, J . A.; Arif, A. M.; Gladysz, J . A. J . Am. Chem.
Soc. 1995, 117, 11922. (b) Brady, M.; Weng, W.; Zhou, Y.; Seyler, J .
W.; Amoroso, A. J .; Arif, A. M.; Bo¨hme, M.; Frenking, G.; Gladysz, J .
A. J . Am. Chem. Soc. 1997, 119, 775. (c) Falloon, S. B.; Szafert, S.;
Arif, A. M.; Gladysz, J . A. Chem. Eur. J . 1998, 4, 1033. (d) Bartik, T.;
Weng, W.; Ramsden, J . A.; Szafert, S.; Falloon, S. B.; Arif, A. M.;
Gladysz, J . A. J . Am. Chem. Soc. 1998, 120, 11071. (e) Dembinski, R.;
Bartik, T.; Bartik, B.; J aeger, M.; Gladysz, J . A. Submitted for
publication (communication: Bartik, T.; Bartik, B.; Brady, M.; Dem-
binski, R.; Gladysz, J . A. Angew. Chem. 1996, 108, 467; Angew. Chem.,
Int. Ed. 1996, 35, 414).
yield.9,12 The 13C NMR coupling constant patterns (J CP
CPt, J CH) allowed unambiguous assignment of the sp
carbon signals.
,
J
(3) (a) Coat, F.; Lapinte, C. Organometallics 1996, 15, 477. (b) Akita,
M.; Chung, M.-C.; Sakurai, A.; Sugimoto, S.; Terada, M.; Tanaka, M.;
Moro-oka, Y. Organometallics 1997, 16, 4882. (c) Bruce, M. I.; Ke, M.;
Low, P. J .; Skelton, B. W.; White, A. H. Organometallics 1998, 17, 3539.
(4) (a) Faust, R. Angew. Chem. 1998, 110, 2988; Angew. Chem., Int.
Ed. 1998, 37, 2825. (b) Bunz, U. H. F.; Rubin, Y.; Tobe, Y. Chem. Soc.
Rev. 1999, 28, 107. (c) Carbon Rich Compounds II: Macrocyclic
Oligoacetylenes and Other Linearly Conjugated Systems; de Meijre, A.,
Ed.; Topics in Current Chemistry 201; Springer-Verlag: Berlin, 1999.
(5) For C16-C32 polyalkynediyl systems with tert-butyl, silyl, or
cyano end groups, see the following lead papers and references
therein: (a) Eastmond, R.; J ohnson, T. R.; Walton, D. R. M. Tetrahe-
dron 1972, 28, 4601. (b) J ohnson, T. R.; Walton, D. R. M. Tetrahedron
1972, 28, 5221. (c) Schermann, G.; Gro¨sser, T.; Hampel, F.; Hirsch, A.
Chem. Eur. J . 1997, 3, 1105.
(6) (a) Hunter, J . M.; Fye, J . L.; Roskamp, E. J .; J arrold, M. F. J .
Phys. Chem. 1994, 98, 1810. (b) Lagow, R. J .; Kampa, J . J .; Wei, H.-
C.; Battle, S. L.; Genge, J . W.; Laude, D. A.; Harper, C. J .; Bau, R.;
Stevens, R. C.; Haw, J . F.; Munson, E. Science 1995, 267, 362. (c)
Homman, K.-H. Angew. Chem. 1998, 110, 2572; Angew. Chem., Int.
Ed. 1998, 37, 2435.
(7) All crystallographically characterized 1,3,5,7-tetraynes (seven)
and 1,3,5,7,9-pentaynes (one) are tabulated in the following papers:
(a) Bartik, B.; Dembinski, R.; Bartik, T.; Arif, A. M.; Gladysz, J . A.
New J . Chem. 1997, 21, 739. (b) Dembinski, R.; Lis, T.; Szafert, S.;
Mayne, C. L.; Bartik, T.; Gladysz, J . A. J . Organomet. Chem. 1999,
578, 229.
(8) (a) The reaction of (COD)PtCl28b and p-tolMgBr (2.5 equiv) gave
(COD)Pt(p-tol)2.8c Subsequent addition of acetyl chloride (1.0 equiv)
in MeOH/CH2Cl2 yielded 1.8d (b) Clark, H. C.; Manzer, L. E. J .
Organomet. Chem. 1973, 59, 411. (c) Alternative synthesis: Eaborn,
C.; Odell, K. J .; Pidcock, A. J . Chem. Soc., Dalton Trans. 1978, 357.
(d) Alternative synthesis: Ertl, J .; Grafl, D.; Brune. H. A. Z. Natur-
forsch. 1982, 37B, 1082.
(9) All new complexes were characterized by IR and NMR spectros-
copy (and many by additional means), as detailed in the Supporting
Information. Most gave correct microanalyses.
(10) Pregosin, P. S.; Venanzi, L. M. Chem. Br. 1978, 276.
(11) (a) Brandsma, L.; Verkruijsse, H. D. Synthesis of Acetylenes,
Allenes and Cumulenes; Elsevier: New York, 1981; p 146. (b) Ibid., p
136.
10.1021/om990448c CCC: $18.00 © 1999 American Chemical Society
Publication on Web 07/30/1999

3262 Organometallics, Vol. 18, No. 17, 1999
Sch em e 1. Syn th eses of P tCxP t Com p lexes
Communications
The oxidative homocoupling of 3 was attempted. The
Eglinton recipe that proved optimal for chiral rhenium
educts (η5-C5Me5)Re(NO)(PPh3)Re(CtC)nH (1 equiv of
Cu(OAc)2 in pyridine)2b,e did not afford detectable
quantities of the target C8 complex trans,trans-(p-tol)-
(p-tol3P)2Pt(CtC)4Pt(Pp-tol3)2(p-tol) (4). However, Hay
conditions (excess O2, 0.20-0.25 equiv of CuCl and
TMEDA in acetone)12b gave 4 in 85% yield after workup
(Scheme 1). The structure followed from the mass
spectral parent ion and spectroscopic properties, which
are discussed with those of homologues below.
Efforts were next directed at compounds with longer
sp carbon chains. As analyzed previously,2e,7 this re-
quires either longer building blocks or “second genera-
tion” chain growth in a metal coordination sphere. Since
higher homologues of 1,3-butadiyne become very ex-
plosive,11b the latter strategy was investigated. As
shown in Scheme 1, 3 and excess HCtCSiEt3 were
subjected to the Hay conditions. Workup gave the
heterocoupling product trans-(p-tol)(p-tol3P)2PtCtCCt
CCtCSiEt3 (5) in 83% yield. Unfortunately, similar
reactions with HCtCCtCSiEt3 gave only homocoupling
products, possibly due to the decreased steric bulk of
the organosilicon partner.
HCtCSiEt3 were reacted under Hay conditions. Work-
up gave the heterocoupling product trans-(p-tol)(p-
tol3P)2PtCtCCtCCtCCtCSiEt3 (8, 48%), sought un-
successfully from 3 and HCtCCtCSiEt3 above. However,
attempts to elaborate 8 to a C16 complex have to date
been unsuccessful, an outcome presently ascribed to the
apparent instability of the corresponding 1,3,5,7-octa-
tetraynyl complex. Finally, PPh3 homologues of 2-7
were similarly prepared (2′-7′), but these exhibited
much lower solubilities. Hence, the Hay couplings were
heterogeneous and required heating, and 13C NMR
spectra were of lower quality.
The monoplatinum complexes Pt(CtC)nX gave n or
n - 1 IR νCtC bands (2176-1991 cm-1). However, the
diplatinum complexes 4/4′ and 7/7′ exhibited n/2 bands,
consistent with their higher symmetry. In all cases, 13
C
NMR spectra showed PtCt signals at 120.9-111.2 ppm.
These were coupled to phosphorus (2J CP 14.8-13.5 Hz)
and platinum (1J CPt 875-650 Hz; satellites). The PtCtC
signals ranged from 98.3 to 96.0 ppm and gave smaller
phosphorus and platinum couplings (<2 and 212-237
Hz). The remaining CtC signals of 7 were at 66.6-56.9
ppm. The colors of 4/4′ and 7/7′ (bright yellow and
orange) were less intense than those of dirhenium
analogues, and UV-visible spectra were less complex.
The two longest wavelength bands intensified and red-
shifted with increasing chain length (nm, CH2Cl2 (ꢀ, M-1
cm-1): 4, 305 (95 000), 343 (100 000); 7, 347 (125 000),
371 (215 000)) but then simply tailed into the visible.
Reaction of 5 with n-Bu4N+F- (1.3 equiv) in wet THF
afforded the 1,3,5-hexatriynyl complex trans-(p-tol)(p-
tol3P)2PtCtCCtCCtCH (6) in 84% yield. A Hay cou-
pling then gave the desired C12 complex trans,trans-(p-
tol)(p-tol3P)2Pt(CtC)6Pt(P-p-tol3)2(p-tol) (7) in 83% yield.
In efforts to further extend the chain, 6 and excess
All compounds exhibited excellent stability, including
a surprising tolerance to O2 in solution. Only concen-
trated solutions of 6 appeared labile. When heated, solid
samples decomposed without melting (4/7, 185/204 °C,
sealed capillary). Cyclic voltammograms of 4 and 7 were
recorded in CH2Cl2. Each showed two irreversible
(12) Related platinum butadiynyl complexes have been similarly
prepared: (a) Fujikura, Y.; Hagihara, N.; Sonogashira, K.; Takahashi,
S.; Toyoshima, N. J . Organomet. Chem. 1978, 145, 101. (b) Bruce, M.
I.; Ke, M.; Low, P. J . J . Chem. Soc., Chem. Commun. 1996, 2405. (c)
AlQaisi, S. M.; Galat, K. J .; Chai, M.; Ray, D. G., III; Rinaldi, P. L.;
Tessier, C. A.; Youngs, W. J . J . Am. Chem. Soc. 1998, 120, 12149.

Communications
Organometallics, Vol. 18, No. 17, 1999 3263
F igu r e 1. Molecular structures of 4′ (top) and 7 (bottom). Key distances (in Å; 4′/7): Pt1-C1, 2.011(4)/1.990(3); Pt1-C10,
2.064(4)/2.060(3); Pt1-P1, 2.3073(11)/2.3055(8); Pt1-P2, 2.3002(11)/2.3164(8); C1-C2, 1.218(6)/1.233(4); C2-C3, 1.368(6)/
1.358(4); C3-C4, 1.223(6)/1.210(5); C4-C4, 1.367(9)/-; C4-C5, -/1.356(5); C5-C6, -/1.211(5); C6-C6, -/1.344(7); Pt1-
Pt1, 12.998(1)/17.9564(4). Key angles (in deg; 4′/7): C1-Pt1-C10, 172.92(19)/177.86(13); P1-Pt1-P2, 178.22(4)/174.45(3);
Pt1-C1-C2, 178.0(4)/174.0(3); C1-C2-C3, 176.5(5)/174.5(4); C2-C3-C4, 177.8(5)/178.6(4); C3-C4-C4, 179.5(9)/-; C3-
C4-C5, -/178.3(4); C4-C5-C6, -/177.5(4); C5-C6-C6, -/178.9(6).
oxidations (V vs ferrocene: 0.96/1.33 and 1.19/1.34) but
no reduction prior to the solvent limit.
parallel chains, the shortest carbon-carbon distances
between which are 8.890 and 7.884 Å, respectively. The
PtC atom of one chain aligns approximately with the
midpoint of the neighbor. This offsets the bulky end
groups, and solvent molecules fill some but not all of
the remaining voids.
In summary, the preceding data establish that me-
dium-length polyynediyl complexes can easily be con-
structed with platinum end groups of the formula
Ar(Ar3P)2Pt. Yields of individual steps are high, and
intermediates and products are especially stable. Fur-
thermore, the ancillary ligands are easily varied. Novel
assemblies derived from such substitutions, as well as
the pursuit of higher chain lengths, will be described
in future reports.
Crystals suitable for X-ray diffraction could be grown
at will, but always with solvent incorporation. Figure 1
shows two structures, 4′ and 7. The bond lengths and
angles about platinum are unexceptional.13 The CtC
and tC-Ct bond lengths in 7 (1.210(5)-1.233(4) and
1.344(7)-1.356(4) Å) are near the upper and lower
extremes of those in 1,3,5,7-tetraynes,7 suggesting
asymptotic approaches to limiting values of ca. 1.24 and
1.34 Å at infinite chain length. The chain in 7 also
curves gracefully. The PtCC and PtCCC angles are the
most bent (174.0(3), 174.5(4)°; others 177.5(4)-178.9(6)°).
Although the platinum-platinum distance (17.9564(4)
Å) is just slightly less than the sum of the intervening
bond lengths (18.06 Å), only one tetrayne shows dis-
tinctly greater nonlinearity.7b Both 4′ and 7 pack with
Ack n ow led gm en t. We thank the NSF and the
Deutsche Forschungsgemeinschaft for support of this
research.
(13) Crystal structures of other trans-(X)(R3P)2PtCtCR complexes:
(a) Furlani, A.; Licoccia, S.; Russo, M. V.; Villa, A. C.; Guastini, C. J .
Chem. Soc., Dalton Trans. 1984, 2197. (b) Lewis, J .; Long, N. J .;
Raithby, P. R.; Sheilds, G. P.; Wong, W.-Y.; Younus, M. J . Chem. Soc.,
Dalton Trans. 1997, 4283. (c) Bohling, J . C.; Peters, T. B.; Arif, A. M.;
Hampel, F.; Gladysz, J . A. In Coordination Chemistry at the Turn of
the Century; Ondrejovic¸, G., Sirota, A., Eds.; Slovak Technical Uni-
versity Press: Bratislava, Slovakia, 1999; p 47.
Su p p or tin g In for m a tion Ava ila ble: Text giving experi-
mental procedures and tables of crystallographic data. This
material is available free of charge via the Internet at
http://pubs.acs.org.
OM990448C