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

Article abstract of DOI:10.1002/chem.202101725

The silylated hexatriynyl complex trans-(C₆F₅)(p-tol₃P)₂Pt(C≡C)₃SiEt₃ (PtC₆TES) is converted in situ to PtC₆H (wet n-Bu₄N⁺ F^?, THF) and cross coupled with the diyne H(C≡C)₂SiEt₃ (HC₄TES; CuCl/TMEDA, O₂) to give PtC₁₀TES (71 %). This sequence is repeated twice to afford PtC₁₄TES (65 %) and then PtC₁₈TES (27 %). An analogous series of reactions starting with PtC₈TES gives PtC₁₂TES (60 %), then PtC₁₆TES (43 %), and then PtC₂₀TES (17 %). Similar cross couplings with H(C≡C)₂Si(i-Pr)₃ (HC₄TIPS) give PtC₁₂TIPS (68 %), PtC₁₄TIPS (68 %), and PtC₁₆TIPS (34 %). The trialkylsilyl species (up to PtC₁₈TES) are converted to 3+2 “click” cycloadducts or 1,4-disubstituted 1,2,3-triazoles trans-(C₆F₅)(p-tol₃P)₂Pt(C≡C)_n-1C=CHN(CH₂C₆H₅)N=N (29–92 % after workups). The most general procedure involves generating the terminal polyynes PtC_xH (wet n-Bu₄N⁺ 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 PtC₂₀TES 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.

Full text of DOI:10.1002/chem.202101725

Accepted Article
Accepted Article
Title: 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
Authors: John A. Gladysz, Hashem Amini, Nancy Weisbach, Sébastien
Gauthier, Helene Kuhn, Nattamai Bhuvanesh, Frank Hampel,
and Joseph H. Reibenspies
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Chem. Eur. J. 10.1002/chem.202101725
Link to VoR: https://doi.org/10.1002/chem.202101725
01/2020

10.1002/chem.202101725
Chemistry - A European Journal
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
[a]
[a]
[a]
[b]
Hashem Amini, Nancy Weisbach, Sébastien Gauthier, Helene Kuhn, Nattamai
[a]
[b]
[a]
*[a]
Bhuvanesh, Frank Hampel, Joseph H. Reibenspies, and John A. Gladysz
Abstract: The silylated hexatriynyl complex trans-(C F )(p-tol P) Pt(CC) SiEt (PtC TES) is
6 5
3
2
3
3
6
+
–
converted in situ to PtC H (wet n-Bu N F , THF) and cross coupled with the diyne H(CC) -
6
4
2
SiEt (HC TES; CuCl/TMEDA, O ) to give PtC TES (71%). This sequence is repeated twice
3
4
2
10
to afford PtC TES (65%) and then PtC TES (27%). An analogous series of reactions starting
14
18
with PtC TES gives PtC TES (60%), then PtC TES (43%), and then PtC TES (17%). Simil-
8
12
16
20
ar cross couplings with H(CC) Si(i-Pr) (HC TIPS) give PtC TIPS (68%), PtC TIPS (68%),
2
3
4
12
14
and PtC TIPS (34%). The trialkylsilyl species (up to PtC TES) are converted to 3+2 "click"
16
18
cycloadducts or 1,4-disubstituted 1,2,3-triazoles trans-(C F )(p-tol P) Pt(CC) C=CHN(CH -
6 5
3
2
n–1
2
C H )N=N (29-92% after workups). The most general procedure involves generating the terminal
6
5
+
–
polyynes PtC H (wet n-Bu N F , THF) in the presence of benzyl azide in DMF and aqueous
x
4
CuSO /ascorbic acid. All of the preceding complexes are crystallographically characterized and
4
the structural and spectroscopic properties analyzed as a function of chain length. Two pseudopo-
lymorphs of PtC TES are obtained, both of which feature molecules with parallel sp carbon
20
chains in a pairwise head/tail packing motif with extensive sp/sp van der Waals contacts.
[a]
Dr. H. Amini, Dr. N. Weisbach, Dr. S. Gauthier, Dr. N. Bhuvanesh, Dr. J. H. Reibenspies,
Prof. Dr. J. A. Gladysz
Department of Chemistry, Texas A&M University,
P.O. Box 30012,
College Station, Texas 77842-3012 [USA]
E-mail: gladysz@mail.chem.tamu.edu
twitter handle: @GladyszJohn
[b]
Dr. H. Kuhn, Dr. F. Hampel
Institut für Organische Chemie and Interdisciplinary Center for Molecular Materials,
Friedrich-Alexander-Universität Erlangen-Nürnberg, Henkestraße 42,
91054 Erlangen, Germany

Supporting Information and the ORCID identification numbers for the authors of this
article can be found under https://doi.org/10.1002/xxxxx.
submitted to Chem. Eur. J.
-1-
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Introduction
[1]
Synthetic approaches to compounds with long sp hybridized carbon chains usually entail
[2,3]
the homocoupling or heterocoupling of polyynyl species.
Most of these involve the generation
of terminal polyynes of the formula Z(CC) H, as sketched in Scheme 1. Such species become
n
[4-8]
increasingly labile as the sp carbon chains are extended.
For the transition metal capped poly-
[6]
[7]
ynes of particular interest in our group, terminal tetraynes L M(CC) H (M = Pt, Re ) may be
y
4
isolated, but only under exacting low temperature conditions. Tykwinski, who has prepared several
[1,8]
extensive series of organic polyynes,
especially with bulky aryl or heteroaryl endgroups, has
isolated adducts of the formula Ar(CC) H with n = 2-7 and spectroscopically characterized high-
n
[8a]
er homologs with n = 8-11.
Z
1/2 Z
n
homocoupling
deprotection
Z
PG
Z
H
n
n
Q
Z'
n'
or
H
Z'
n'
heterocoupling
Z'
Z
n'
n
Scheme 1. The most common reaction types used to construct the sp carbon backbone of long conjugated polyynes.
From a number of standpoints, there continues to be great interest in the synthesis and
physical characterization of compounds with long polyyne chains. For example, they provide mo-
dels for the elusive polymeric sp carbon allotrope, often termed carbyne, for which a number of
[9]
extraordinary physical properties (e.g., tensile stiffness, specific strength) have been predicted.
[10]
They have also attracted much attention in molecular electronics and optoelectronics.
More
exact information regarding the accessibility and persistence of labile terminal polyynyl building
blocks Z(CC) H would be tactically advantageous in developing these and allied fields.
n
-2-
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[11]
[12]
Some time ago, we communicated
the viability of effecting "click" reactions
with
platinum terminal polyynyl complexes of the formula trans-(C F )(p-tol P) Pt(CC) H (n = 2-6),
6 5
3
2
n
henceforth denoted PtC H (x = 2n). This was part of a broader effort involving click reactions in
x
[13]
[14,15]
metal coordination spheres,
a topic for which there are now many contributors.
The "par-
ent" transformation, involving benzyl azide and the easily isolated butadiynyl complex PtC H, is
4
depicted in Scheme 2. For n = 3-6 (x = 6/8/10/12), the terminal polyynes were generated in situ
under special conditions from the corresponding triethylsilyl polyynes trans-(C F )(p-tol P) Pt-
6 5
3
2
(CC) SiEt (PtC TES). However, this protocol was not extended to higher homologs that repre-
n
3
x
[8]
sent the frontier of polyyne chemistry today.
Scheme 2. The title reaction carried out on an isolable butadiynyl complex.
Accordingly, in this full paper we (1) provide a complete account of the work communic-
[11]
ated earlier,
(2) demonstrate the applicability of the click trapping reaction to platinum com-
plexes that have longer sp carbon chains (n = 7-9) and/or been derived from alternative trialkylsilyl
endgroups, (3) detail iterative sp chain extension procedures for accessing the click substrates, and
(4) report crystal structures for all isolable complexes, thus realizing a complete catalog of structur-
al trends and packing motifs throughout the chain lengths investigated. Unsurprisingly, click che-
[16]
mistry has also been applied to organic terminal polyynes, but only through pentaynes (n = 5).
Finally, this work helps set the stage for the preparation of polyynediyl adducts that would rival
[8]
the longest characterized to date (n = 22, 24).
Results
Syntheses of PtC SiR . Reliable procedures for lengthening the sp carbon chains of com-
x
3
[5b]
plexes with Pt(CC) SiR units by four atoms have been previously developed.
These entail
n
3
an initial protodesilylation to an intermediate Pt(CC) H species, followed by a Hay or Glaser-
n
[2b,3]
Hay oxidative heterocoupling (CuCl/TMEDA, O )
with a silylated butadiyne H(CC) SiR .
2 3
2
-3-
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Scheme 3. Syntheses of educts for the title reaction.
-4-
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[5b,7,17]
Usually R is ethyl or isopropyl; both building blocks are readily available.
Two aspects of
this procedure merit emphasis. First, a significant excess of H(CC) SiR is required to render
2
3
homocoupling of the Pt(CC) H intermediate less probable. Nonetheless, in nearly all cases some
n
diplatinum or Pt(CC) Pt adduct can be detected. Second, due to the enhanced lability of the
2n
[18]
Pt(CC) H intermediate with increased sp chain length, yields tend to gradually diminish.
Al-
n
though it may not be directly relevant to this trend, the Brønsted acidities of terminal polyynes
[19]
increase with chain length.
Accordingly, the platinum complexes employed in this study were accessed by the chain
[5a]
[5a]
extension reactions in Scheme 3. These use PtC TES
and PtC TES,
which are themselves
6
8
substrates for the title reaction, as springboards. In all of these sequences, the initial addition of a
+
–
commercial wet THF solution of n-Bu N F is believed to generate the terminal polyyne PtC H.
4
x
The subsequent addition of Me SiCl has proved beneficial when conducting subsequent oxidative
3
[5]
homocouplings.
The sequential elaboration of PtC TES to PtC TES and then PtC TES using H(CC) -
6
10
14
2
SiEt or HC TES could be effected in 71% and 65% yields, respectively, after workups. PtC -
3
4
10
TES was similarly elongated using H(CC) Si(i-Pr) or HC TIPS to the adduct PtC TIPS
2
3
4
14
[20]
(68%). The lower homologs PtC TIPS and PtC TIPS have been previously reported.
Next,
8
12
PtC TES was analogously converted to PtC TES, but with a noticeable diminution in yield
14
18
(27%).
In a parallel sequence (Scheme 3, bottom), PtC TES was similarly elaborated to PtC -
8
12
TES (60%, using HC TES) and PtC TIPS (68%, using HC TIPS). Both were analogously tak-
4
12
4
[20]
en on to PtC TES (43%) and PtC TIPS (34%), respectively. As reported elsewhere,
analogs
of some of these TIPS species with p-tolyl platinum ligands in place of the pentafluorophenyl
groups have also been prepared. Finally, PtC TES and HC TES were similarly condensed to
16
16
16
4
give PtC TES (17%), but again with a substantial drop-off in yield.
20
All of the trialkylsilyl polyynyl complexes were isolated as air stable powders. They were
1
13 31
characterized by NMR ( H, C, P), IR, and UV-visible spectroscopy and microanalyses, as de-
-5-
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Chemistry - A European Journal
tailed in the experimental section. Key data are summarized in Tables 1-3 and analyzed in the
discussion section. PtC TES was yellow-orange, and the colors deepened with increasing sp car-
10
bon chain length, reaching orange-red with PtC TES. When exposed to ambient light, PtC TES
20
14
and longer chain homologs discolored over the course of several days, but the triisopropylsilyl
analogs appeared more robust.
Click chemistry. Scheme 2 depicts the title reaction as carried out with the only easily
isolated terminal polyyne in this series, PtC H. Aqueous CuSO /ascorbic acid is a standard rec-
4
4
[12]
[21]
ipe
for generating the Cu(I) needed to catalyze the 3+2 cycloaddition.
DMF is frequently
employed as a (co)solvent, and benzyl azide as a reaction partner. The product trans-(C F )((p-
6 5
tol) P) PtCCC=CHN(CH C H )N=N (PtC HN Bz) was isolated by silica gel chromatography,
3
2
2 6
5
4
3
as were all higher homologs below.
Next, the viabilities of all the polyynes in Scheme 3 as substrates for protodesilylation/click
sequences were evaluated. First, THF solutions of PtC TES and PtC TES were treated with wet
6
8
+
–
n-Bu N F in THF, analogously to the initial step at each stage in Scheme 3, followed by Me Si-
4
3
Cl. A DMF solution of benzyl azide and aqueous solutions of CuSO and ascorbic acid were then
4
added. This protocol is henceforth referred to as "procedure A". As shown in Scheme 4, workups
gave the click adducts PtC HN Bz and PtC HN Bz in 70% and 60% yields, respectively. How-
6
3
8
3
ever, when the same sequence was attempted with PtC TES, no tractable products could be iso-
10
lated.
To enhance trapping efficiency, it was sought to generate PtC H in the presence of all
10
components required for the click cycloaddition. Thus, a THF solution of PtC TES was combin-
10
ed with a DMF solution of benzyl azide (1.5-2.0 equiv), and aqueous CuSO and ascorbic acid
4
+
–
were added. Only then was the wet THF solution of n-Bu N F introduced to cleave the silicon-
4
carbon bond. This protocol, termed "procedure B", gave the target complex PtC HN Bz in 92%
10
3
yield after workup.
It was next verified that "procedure B" could be successfully used to convert PtC TES to
6
PtC HN Bz and PtC TES to PtC HN Bz (62% and 85%, respectively). Then the important
6
3
8
8
3
-6-
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P(
Pt
P(
p
p
-tol)3
-tol)3
Procedure A1: 1. wet n-Bu4N+ F- , THF
SiR3
n-2
2. Me3SiCl
F5
Procedure A2: CuSO4 and ascorbic acid, H2O
Procedure A1: n = 3-4
or
Procedure B: n = 3-9
in DMF
N3
P(
Pt
P(
p
p
-tol)3
-tol)3
in DMF
Procedure B: 1. THF,
N3
H
n-2
F5
2. CuSO4, ascorbic acid, H2O
3. wet n-Bu4N+ F-
Procedure A2: n = 3-4
(or continue
Procedure B)
P(
Pt
P(
p
p
-tol)3
-tol)3
N
N
N
F5
PtC6HN3Bz (70 % (A), 62 % (B))
P(
Pt
P(
p
p
-tol)3
N
N
N
F5
F5
F5
F5
F5
F5
-tol)3
PtC8HN3Bz (60 % (A), 85 % (B))
-tol)3
P(
Pt
P(
p
p
N
N
N
-tol)3
PtC10HN3Bz (<2 % (A), 92% (B))
P(
Pt
P(
p
p
-tol)3
N
N
N
-tol)3
PtC12HN3Bz (81% (B))
P(
Pt
P(
p
p
-tol)3
N
N
N
-tol)3
PtC14HN3Bz (from PtC14TES 43% (B), from PtC14TIPS 52% (B))
P(
Pt
P(
p
p
-tol)3
N
N
N
-tol)3
PtC16HN3Bz (from PtC16TES 54% (B), from PtC16TIPS 64% (B))
-tol)3
P(
Pt
P(
p
p
N
N
N
-tol)3
PtC18HN3Bz (from PtC18TES 29% (B))
Scheme 4. Syntheses of title complexes.
-7-
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question of trapping efficacy with higher homologs was addressed. As shown in Scheme 4, the
same conditions could be applied to the entire range of educts PtC TES, with the yields of click
x
adducts PtC HN Bz varying from 81% to 43% to 54% to 29% as x increased from 12 to 14 to 16
x
3
to 18. No experiment was carried out with PtC TES, as the amount of sample was smaller and
20
the entire quantity was employed for additional (successful) homocoupling and heterocoupling
reactions, as will be reported later.
The same recipe could be successfully applied to the triisopropylsilyl species PtC TIPS
14
and PtC TIPS. As shown in Scheme 4, the cycloadducts PtC HN Bz and PtC HN Bz were
16
14
3
16
3
isolated in 52% and 64% yields, respectively. Thus, the average yields vary from ca. 43% to 92%
as procedure B is applied to substrates with x = 6 to 16. Only at x = 18 is a significant diminution
encountered (29%). However, optimization strategies such as the effect of lower temperatures re-
main to be examined.
The click products in Scheme 4 were air stable solids and characterized analogously to the
complexes in Scheme 3 (see experimental section). Their colors deepened with increasing sp chain
length (PtC HN Bz, yellow; PtC HN Bz, dark red), and PtC HN Bz and PtC HN Bz dis-
8
3
18
3
16
3
18
3
colored over several days when exposed to ambient light. The UV-visible spectra, of relevance to
these observations, are depicted in Figure 1. Other key spectroscopic properties are summarized
in Tables 1-3 and analyzed in the discussion section.
Figure 1. UV-visible spectra of PtC HN Bz in CH Cl . The quantity of PtC HN Bz employed did not allow an
x
3
2
2
18
3
accurate determination of .
-8-
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Figure 2. Thermal ellipsoid plots (50% probability) of the molecular structures of PtC TES.
x
-9-
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Structural Data. Surprisingly, crystals of all of the preceding complexes or solvates there-
of could be grown, at least by coworkers gifted with a "sixth sense" for such endeavors. The X-
ray structures were solved as described in the experimental section. The molecular structures are
grouped in Figures 2-4, and key data are summarized in Tables 4-6 and s1-s4 (Supporting
Information). The crystals of PtC TES and PtC TIPS·(CH Cl ) exhibited two independent
12
12
2
2 0.5
molecules in the unit cell. Only one structure is provided in Figures 2 and 3, but data are tabulated
for both.
Figure 3. Thermal ellipsoid plots (50% probability) of the molecular structures of PtC TIPS.
x
In a fortunate development, the complex with the longest sp carbon chain, PtC TES,
20
[22]
could be crystallized as two pseudopolymorphs
belonging to different space groups (P−1,
P2 /c). One was a CH Cl hemisolvate, and the other a monosolvate. Only the former is depicted
1
2
2
in Figure 2, but data for both are tabulated and treated further below. A few atoms of PtC -
12
TIPS·(CH Cl ) , PtC TES, PtC TIPS, and both forms of PtC TES were disordered, but
2
2 0.5
16
16
20
-10-
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Figure 4. Thermal ellipsoid plots (50% probability) of the molecular structures of PtC HN Bz.
x
3
-11-
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this could be modeled as described in the experimental section. Data are given only for the domin-
[23]
ant conformation, except in the case of PtC TES·(CH Cl ), where there was a 51:49 ratio
20
2
2
and both are fully described.
There have been extensive analyses of the geometrical features of long conjugated poly-
[24]
ynes,
and this study adds an abundance of structures (eighteen independent molecules) to this
literature. Accordingly, key attributes are scrutinized in the discussion section. For an interim per-
spective, the longest sp carbon chain in other crystallographically characterized platinum complex-
[20]
es would be the decayne in PtC Pt.
This adduct could be prepared in 86% yield from PtC -
10
20
TIPS via the oxidative homocoupling of transient PtC H. The crystal structure of one other deca-
10
[25]
yne, t-Bu(CC) t-Bu, has been reported,
but none so far for higher polyynes. Thus, PtC TES
20
10
represents the first unsymmetrically substituted decayne to be structurally characterized. The cryst-
al structures of the shorter chain complexes PtC HN Bz and PtC HN Bz, which were presented
4
3
6
3
[11]
in the communication,
are not further treated here. The crystal structures of PtC TES, PtC -
6 8
[20,26]
TES, PtC TIPS, and PtC TIPS have been described in earlier studies.
6
8
Discussion
Syntheses of title complexes. As summarized in Scheme 3, this work has significantly
expanded the availability of the trialkylsilyl polyynyl building blocks PtC SiR (x = 10/12/14/16/
x
3
18/20). These in turn provide entries to monoplatinum and diplatinum complexes with still longer
[20]
polyyne chains, such as the recently reported PtC Pt.
The methodology involves an initial
24
protodesilylation of a precursor PtC SiR to PtC H, as supported by the click reaction port-
x-4
3
x-4
folio in Scheme 4, followed by Hay cross coupling reactions with HC SiR . In line with other
4
3
[20]
studies,
there seems to be no significant advantage of triisopropylsilyl as opposed to triethylsi-
lyl coupling partners. Complementary iterative chain extension protocols involving haloalkynes
[8c]
X'(CC) SiR (X' = Br, I; n = 1-3) are nicely illustrated in recent work of Tykwinski,
and
n
3
similar methodology could well be applicable to these platinum complexes.
In a related series of platinum complexes in which the pentafluorophenyl groups have been
[5b]
replaced by p-tolyl ligands,
protodesilylation rates have been shown to increase with sp chain
-12-
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lengths, probably for reasons connected to the Brønsted acidity trends of terminal polyynes noted
[19]
above.
Qualitative observations suggest parallel behavior in Schemes 3 and 4, and the possibili-
ty of more efficient click trapping reactions at lower temperatures. In preliminary efforts, analog-
ous coupling reactions involving PtC SiR and the tetraynes HC SiR have been investigated.
x
3
8
3
However, these have so far proved challenging to control in that multiple condensation products
(incorporating two or more tetraynes) are often produced. Such byproducts are rarely encountered
with the diyne building blocks HC SiR .
4
3
On a yield basis, the trapping of PtC H and higher homologs by benzyl azide under click
10
conditions is more efficient than with HC SiR under Hay conditions. Unfortunately, the click
4
3
adducts represent dead ends with respect to sp carbon chain extension. However, they remain sub-
strates for other types of transformations, such as N- or C-functionalization of the triazole moi-
[13]
ety.
In the most relevant contribution from another research group, Veige has shown that platin-
um ethynyl complexes can similarly react, as exemplified by the two-fold click adduct in Scheme
[14g]
5.
A number of related species were also reported.
PEt3
PEt3
Pt
N3
N
N
N
N
N
N
H
Pt
H
CuOAc, CH2Cl2
89%
PEt3
PEt3
mixture of syn and anti atropisomers
Ph2
P
Ph2 P
(OC)2Co
(CO)
Co
2
W
(CO)3
C
Co(CO)3
1
Scheme 5. Other relevant reactions and complexes.
The complexes PtC SiR , PtC TES, PtC TES, and PtC HN Bz represent some of
16
3
18
20
18
3
the longest unsymmetrically substituted polyynes isolated to date. Particularly relevant would be
the tungsten/tricobalt complex with a (CC) segment shown in Scheme 5 (1), which Bruce access-
9
[27]
ed by a novel three component condensation.
Tykwinski has isolated species of the formula
ArC TIPS, where x = 18/20/22/24 and Ar represents t-butyl substituted trityl or diaryl-4-pyridinal
x
[8a,c]
moieties.
Finally, several investigators who have carried out Hay coupling reactions with long
-13-
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10.1002/chem.202101725
Chemistry - A European Journal
[28]
polyynes have noted minor byproducts derived from the loss of two sp carbon atoms,
even
when impurities in the educts can be rigorously excluded. Traces of such species were sometimes
noted in the mass spectra of products from Schemes 3 and 4, but were normally not detectable by
NMR.
Thermal and spectroscopic properties. As noted above, all of the complexes prepared in
Schemes 3 and 4 are stable for periods of days in air, but thermolyses in open capillaries reveal
some relatively low onsets of decomposition (50-60 °C for six complexes; see experimental sec-
tion), with only two above 150 °C (PtC HN Bz, PtC HN Bz). The triisopropylsilyl adducts were
6
3
8
3
more robust than triethylsilyl analogs. In the polyyne literature, bulkier and more electropositive
[1,5,7,8,20,25,27,29,30]
endgroups generally lead to greater shelf stabilities.
13
1
Table 1 summarizes the C(sp) C{ H} NMR signals of PtC SiR and PtC HN Bz. The
x
3
x
3
full observation of these intrinsically weaker absorptions is challenging, especially given the inten-
31
195
sity compromising P or
Pt couplings associated with the PtCCC resonances (normally re-
[20]
solved only under optimized conditions),
and the unsymmetrically substituted termini. The Pt-
CC and CCSi signals of PtC SiR can be reliably assigned from chemical shifts, the latter aided
x
3
13
[30]
[20,31]
by C labeling experiments of Tykwinski.
Also, as demonstrated in a recent study,
DFT
calculations can nail down nearly all other C(sp) assignments. The PtCC and CCSi signals shift
progressively downfield with chain length (108.2 to 111.3 ppm and 84.9 to 88.2 ppm), and the
PtCC and CCSi signals upfield (95.2 to 94.9 ppm and 89.8 to 88.9 ppm). In the series PtC HN -
8
3
13
Bz to PtC HN Bz, the PtCC C NMR signals exhibit analogous chemical shift trends (108.0
18
3
2
to 111.0 ppm and 95.4 to 94.9 ppm), and the C(sp ) C=CH peaks also vary monotonically (131.1
to 129.4 ppm; 127.1 to 128.8 ppm). With all such sequences, the properties of the corresponding
PtC polymers can be estimated by extrapolating to the asymptotic limit.

31
1
As shown in Table 2, the P{ H} NMR signals for each series of complexes shift modestly
downfield as the sp chains lengthen. However, the values become essentially constant at longer
1
chain lengths (e.g., 18.02-18.04 ppm for PtC TES with x = 14, 16, 18, 20). The J values are
x
PPt
[32]
in accord with the trans geometries,
and generally decrease with increasing chain lengths. This
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trend is easily seen with PtC HN Bz, as the values are more differentiated for shorter chains, or
x
3
[5a,20]
by including previously reported data for PtC TES and PtC TES.
The IR data in Table 2
show that, as found with all families of conjugated polyynes, the numbers and intensities of IR
bands increase with chain length.
6
8

C≡C
As summarized in Table 3, the UV-visible spectra of PtC SiR and PtC HN Bz exhibit
x
3
x
3
increasing numbers of progressively more intense and red shifted absorptions, consistent with the
color trends noted above. These are illustrated for PtC HN Bz in Figure 1. As would be expected,
x
3
the 
and molar extinction coefficients () of PtC TES and PtC TIPS are quite similar for
max
x
x
–1 –1
equal values of x (14, 16). The  values reach as high as 216000 M cm with PtC TES, but
20
[5,20]
remain somewhat less than for related complexes with PtC Pt linkages.
Time dependent DFT
x
calculations on model diplatinum complexes show that the intense longer wavelength absorptions
[33]
acquire increasing HOMO → LUMO character as the sp chains lengthen.
For eight complexes,
three weak bands at even longer wavelengths can also be detected (PtC TES, x = 10, 12, 14;
x
PtC TIPS; PtC HN Bz, x = 10, 12, 14, 16). By analogy to the spectra of other conjugated poly-
14
x
3
[5b,8c,34]
ynes,
these can be attributed to CC vibrational fine structure. As a specific example, the
–1
band spacings for PtC HN Bz (430, 467, 511 nm) correspond to 1842-1844 cm . The average
16
3
–1
over all complexes is 1875 cm . These absorptions are associated with a second class of transi-
tions that become less intense at longer chain lengths, with decreasing HOMO → LUMO charac-
[33]
ter
.
Molecular structures. In any series of polyynes, bond length trends are of intrinsic inter-
est, as distances in the polymer carbyne can be extrapolated with increasing confidence as the
macromolecular limit is approached. However, the esd values associated with the bond lengths
[24]
and angles of polyyne crystal structures
are often too large for meaningful comparisons, either
within or between molecules. Various averaging algorithms, such as for PtC TES and PtC TIPS
x
x
with identical values of x, can give increased statistical confidence. However, modern computa-
tional methods often provide superior insight regarding trends.
In this context, consider the platinum-carbon bond lengths, which are the most accurately
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10.1002/chem.202101725
Chemistry - A European Journal
determined crystallographically. In the diplatinum series PtC Pt, DFT calculations on model com-
x
[33]
plexes predict a 0.4% contraction as x is increased from 4 to 26 (2.039 Å to 2.031 Å).
As shown
in Table 6 for the click adducts PtC HN Bz, there is a statistically significant contraction from
x
3
2.035(10) to 1.977(4) Å as x is increased from 8 to 18 (6 and 16 sp carbon chains). Furthermore,
[11]
the platinum-carbon bond in the lower homolog PtC HN Bz is longer yet (2.094(14) Å).
How-
6
3
ever, the bond length in PtC HN Bz (1.935(7) Å) is shorter than that of PtC HN Bz (1.977(4)
16
3
18
3
Å), and those in PtC HN Bz, Pt HN Bz, and PtC HN Bz are not meaningfully differentiated
10
3
12
3
14
3
(1.989(5)-1.980(3) Å). The platinum-carbon bond lengths of PtC SiR can be similarly bookend-
x
3
ed, contracting from 2.000(9) Å in PtC TES to 1.978(6) Å in one pseudopolymorph of PtC -
10
20
TES (Tables 4, 5). However, there are again seeming irregularities, with the magnitudes of the esd
values often limiting rigorous comparisons.
There is greater uncertainty with crystallographic carbon-carbon bond distances. The com-
putations noted above predict a 0.5% elongation of the PtCC bond (1.233 Å to 1.239 Å), or a
[33]
1.5% contraction of the PtCC-C bond (1.366 Å to 1.345 Å), as x is increased from 4 to 26.
Manifestations of both trends can be seen in the data for PtC HN Bz (Table 6). The PtCC bonds
x
3
lengthen from 1.158(13) Å (x = 8) to 1.281(9) Å and 1.226(6) Å (x = 16, 18). The PtCC-C bonds
contract from 1.386(14) Å (x = 8) to 1.333(8) Å and 1.350(6) Å (x = 16, 18). Although trends are
[35]
less pronounced relative to the esd values with PtC SiR , behavior appears to be parallel.
x
3
The experimental CC and C-C bond lengths in polyynes have also been analyzed in
[36]
[8c,25]
the context of BLA (bond length alternation)
parameters.
BLA is defined as the differ-
avg
ence between the average carbon-carbon single bond lengths and triple bond lengths, and values
for the platinum complexes are summarized in Tables 4-6. For the parent parameter, BLA, the
central carbon-carbon bond is first considered (CC for odd n; C-C for even n). Then the
average distance for the two adjacent bonds is subtracted, and the absolute value taken as the BLA.
In the series of crystallographically characterized organic polyynes t-Bu(CC) t-Bu (n =
n
[8c,25]
2, 3, 4, 5, 6, 8, 10),
these parameters monotonically decrease towards non-zero asymptotic
limits with increasing n (BLA(avg) 0.145 Å), implying persistent bond length alternation in car-
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Chemistry - A European Journal
byne. However, for PtC SiR and PtC HN Bz the parameters vary essentially randomly (BLA
x
3
x
3
(avg) 0.158 to 0.121 Å for n > 4). Perhaps the unsymmetrical substitution complicates such analys-
es. However, we suggest that the bulky platinum endgroups, which engender a variety of steric
and electronic interactions (vide infra), give rise to packing forces that distort the bond length
patterns from those that would be expected in the gas phase.
The conformations exhibited by the sp carbon chains in Figures 2-4 belong to previously
[24]
recognized motifs (e.g., bow-shaped, s-shaped, random)
set by patterns in bond and torsion
angle sequences. Given the weak force constants associated with bending alkyne or polyyne bond
[33,37]
angles below 180°,
these are viewed as originating from packing forces. In Tables 4 and 5,
the platinum-silicon distances are compared to the sum of the intervening bond lengths. The former
exhibit only 0.6-2.5% contractions (average 1.4%; maximum in PtC TES), indicative of less
18
extreme distortions than in previously characterized complexes (e.g., 6.2% in a PtC Pt adduct).
12
[5a,24]
The average contraction in PtC HN Bz (Table 6) is slightly less (0.9%) when considering
x
3
2
platinum and the C=CH (C(sp )) carbon termini and complexes with at least eight sp carbon atoms
(x > 10). The average bond angles are also given in Tables 4-6, but they do not vary greatly (178.3-
176.0°; average 177.0°) or correlate to conformations or contractions.
As is easily seen in Figures 2-4, all crystal structures exhibit π stacking between the penta-
fluorophenyl ligands and p-tolyl groups of the phosphine ligands. Attractive C F /C H  interac-
6 5
6 5
[38]
tions have been documented in numerous molecules and crystal lattices,
including other poly-
[34a]
[5a,6,13,20,26]
ynes,
and may be a factor in the superior crystallinity of this series of complexes.
In half of the cases, two p-tolyl groups engage, giving a three-ring "sandwich" motif with centroid-
centroid distances of 3.42 Å to 3.90 Å as summarized in Tables 4-6. Related metrical parameters
include the angle defined by the three centroids (140.7°-162.5° or 158.1° average), and the two
C
-P-Pt-C
torsion angles (±0.1° to ±16.1° in complexes with three-ring stacks, indicating
ipso
ipso
nearly eclipsed -C
bonds). In nine complexes (one independent molecule of both PtC TES
12
ipso
and PtC TIPS; PtC TES, PtC TIPS, PtC TES, PtC TIPS, PtC TES, PtC HN Bz, Pt-
12
14
14
16
16
18
8
3
C HN Bz), there is only one strong C F /C H CH interaction, with the second p-tolyl group
14
3
6 5
6
4
3
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10.1002/chem.202101725
Chemistry - A European Journal
exhibiting centroid-centroid distances of 3.993-4.060 Å (weakly interacting) or 4.205-4.464 Å
(non-interacting). For five of the six molecules in the latter category, one C -P-Pt-C
torsion
ipso
ipso
angle is far outside the range of the others (±33.6° to ±38.3°).
Lattice structures. In general, the monoplatinum complexes in Schemes 3-4 are much
easier to crystallize than diplatinum analogs with identical sp carbon chain lengths. Although the
[20]
decayne PtC Pt can be crystallized as a ~monosolvate,
the hexayne PtC Pt can only be
20
12
[5a]
obtained as a pentasolvate, and the octayne PtC Pt as a decasolvate.
In contrast, most of the
16
structures described herein are unsolvated, and for only one is more than a single solvent molecule
present (PtC HN Bz·(C H ) ). Given the sample size, these observations can be taken as evid-
16
3
6 14 2
ence that unsymmetrically substituted monoplatinum polyynes usually have access to more effici-
ent packing motifs with presumably higher lattice energies.
For another generalization, consider the five pairs of trialkylsilyl polyynyl complexes Pt-
[20,26]
C TES and PtC TIPS (x = 6, 8, 12, 14, 16), the first two of which were reported earlier.
x
x
Identical space groups are found for each value of x, as shown in Tables s2 and s3 for the last three
(all P-1 with Z = 2 except for PtC SiR which are P2 /n with Z = 8). The unit cell dimensions
12
3
1
and volumes of each pair are comparable, but incrementally greater in the complexes with larger
triisopropylsilyl endgroups. Accordingly, the packing motifs of the individual molecules are quite
similar. Thus, the triethylsilyl and triisopropylsilyl adducts afford analogous crystal lattices.
[24]
The packing motifs of crystalline polyynes have been analyzed in considerable detail,
and several recurring patterns have been noted. One of the most common features two non-parallel
sets of parallel sp carbon chains. Given the non-linear conformations evident in Figures 2-4, paral-
lel is judged with respect to the vectors defined by the terminal substituents (platinum and silicon
for PtC SiR ). A typical example is provided by PtC HN Bz, depicted in Figure 5 (top) with
x
3
14
3
the phosphine ligands omitted. To help differentiate the two sets of sp chains, one is rendered in
turquoise.
[39]
The van der Waals radius of a sp carbon atom is usually taken as 1.78 Å,
and the shortest
C(sp)-C(sp) distance between parallel chains is 3.605 Å. Thus, each sp chain is nearly in van der
-18-
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Waals contact with its neighbor. In all cases, there is a head-to-tail arrangement, offset or "out of
registry" by six sp carbon atoms, such that the closest distances occur over the next six sp atoms
(3.605-3.706 Å; average 3.660 Å). A similar motif is exhibited by PtC HN Bz (offset of five sp
16
3
atoms with closest distances over the next nine). Now the C(sp)-C(sp) distances are shorter (3.387-
3.433 Å; average 3.405Å), perhaps due in part to the lengthened chain/chain overlap.
Figure 5. Packing of crystalline PtC HN Bz (top) and PtC TES (bottom) with hydrogen atoms and P(p-tol)
3
14
3
16
ligands omitted. The turquoise atoms highlight the second set of parallel sp carbon chains in the former.
Packing motifs in which all sp carbon chains are parallel are also common. One example
is provided by PtC TES, illustrated in Figure 5 (bottom). The nearest sp chains again show a
16
head-to-tail arrangement, with an offset of five atoms such that eleven are quite close, with C(sp)-
C(sp) distances of 3.562-3.854 Å (average 3.658 Å). Crystalline PtC TES also exhibits closely
18
spaced parallel chains with an offset of nine atoms (C(sp)-C(sp) for seven nearest atoms 3.690-
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3.880 Å; average 3.769 Å). However, PtC TES features two non-parallel sets of parallel chains
10
that lack any van der Waals contact, within or between the sets (shortest C(sp)-C(sp) distance
5.063 Å).
Figure 6. Top: packing of crystalline PtC TES·(CH Cl ) with hydrogen atoms, P(p-tol) ligands, and solvate mol-
20
2
2
3
ecules omitted. The sp carbon chains are disordered, and only the major conformer is depicted. The two sets of par-
allel carbon chains are shown in grey and turquoise. Bottom: both sp carbon chain conformations, with regions of
closest C(sp)-C(sp) distances boxed. The upper grouping corresponds to sp chains given in grey in the top.
The lattices of the two pseudopolymorphs of the complex with the longest sp carbon chain,
PtC TES, are of special interest. As shown in Figure 6 (top), the monosolvate PtC TES·(CH -
20
20
2
Cl ) exhibits two non-parallel sets of parallel chains. However, analysis is complicated by disorder
2
over nine sp carbon atoms, which as noted above could be successfully modeled as a 51:49 mixture
[23]
of two conformers.
Both are offset by four carbon atoms. In the lattice of the major conformer,
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magnified in the bottom of Figure 6, there are five shorter C(sp)-C(sp) distances of 3.736-3.625 Å
(avg 3.671 Å), and, reflecting a gradual curvature, six pairs of atoms separated by 4.031-4.322 Å.
In the minor conformer, the sp chains distort in opposite directions such that they become
closer to different sp chains in the lattice (Figure 6, bottom, lower grouping). This underscores a
feature that is difficult to convey in the packing diagram – namely, that all parallel chains are close
to being within continuous van der Waals contact. Thus, returning to the major conformer, C(sp)-
C(sp) distances involving the second nearest chain are as short as 4.246-4.612 Å. With the minor
conformer, eleven carbon atoms exhibit C(sp)-C(sp) distances of 3.971-2.769 Å (average 3.194
Å). Those less than 3.2 Å are likely artifacts associated with modeling the disorder, so further
analyses are not attempted. However, due to curvature associated with the SiEt terminus, the
3
SiC(sp)-C(sp) distance in the minor conformer becomes greater than that in PtC TES in Figure
16
5 (5.077 Å vs. 3.854 Å). Finally, the sp carbon chain mobility in Figure 6 hints at decomposition
mechanisms that may become operative at higher temperatures or longer chain lengths.
In contrast to the monosolvate, the lattice of the hemisolvate PtC TES·(CH Cl ) exhi-
20
2
2 0.5
bits only parallel sp chains. As depicted in Figure 7, each is in van der Waals contact with one
neighbor, offset by four carbon atoms. The shorter C(sp)-C(sp) distances extend over fifteen atoms
(3.983 to 3.426 Å; average 3.571 Å), a much greater span than in the monosolvate. Some curvature
associated with the SiEt termini is apparent, as reflected by the SiC(sp)-C(sp) distance (4.240 Å).
3
The closest C(sp)-C(sp) distances associated with the next two nearest sp chains are >5.8 Å and
>6.7 Å,
Figure 7. Packing of crystalline PtC TES·(CH Cl ) with hydrogen atoms, P(p-tol) ligands, and solvate
20
2
2 0.5
3
molecules omitted.
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Despite the different packing motifs of the pseudopolymorphs PtC TES·(CH Cl ) and
20
2
2 0.5
3
PtC TES·(CH Cl ), the overall densities are comparable (1.431 vs. 1.423 Mg/m ; Table s1).
20
2
2
Interestingly, the lattice of the diplatinum decayne PtC Pt·(CH Cl ) , which features two non-
20
2
2 0.8
3 [20]
parallel sets of parallel chains, exhibits a somewhat higher density (1.508 Mg/m ).
However,
the closest C(sp)-C(sp) distance is 6.464 Å.
Conclusion. This study has demonstrated the ability of the classic click 3+2 organoazide
cycloaddition to serve, under appropriate conditions, as a "coal miner's canary" for the detection/
trapping of labile Pt(CC) H species that are critical intermediates in the pursuit of extremely
n
challenging synthetic targets. These efforts required a number of precursors with Pt(CC) SiR
n
3
segments, for which systematic synthetic protocols have been developed. As a collateral benefit,
the crystal structures of all of these precursors and click adducts could be determined, providing
valuable additions to the rather meager catalog of structurally characterized polyynes with longer
sp chain lengths. Finally, this work sets the stage for a systematic investigation of homocoupling
reactions of the labile Pt(CC) H species, including still higher homologs. These results will be
n
reported in due course.
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Experimental Section
General Data. All reactions were performed under dry N atmospheres using conventional
2
Schlenk techniques, but workups were carried out in air. Instrumental methods and other protocols
[6,20]
have been described in earlier papers in this series (see also the Supporting Information).
The homologous series of reactions in Schemes 3 and 4 were not carried out under identical
conditions, due in part to the number of coworkers who participated in this study. However, the
differences as the sp carbon chain lengths are extended are relatively minor. Given the lengthy
description needed in each case, only representative procedures (one for a shorter sp chain and
another for a longer) are provided below. Full details for all of the syntheses, and all characteriza-
tion data, are given in an unbroken aggregate block in the Supporting Information.
trans-(C F )(p-tol P) Pt(CC) SiEt (PtC TES). A three-neck round bottom flask
6 5
3
2
5
3
10
[5a]
was fitted with a gas dispersion tube, charged with PtC TES (0.930 g, 0.803 mmol)
and THF
6
(90 mL), and cooled to  °C. A Schlenk flask was charged with CuCl (0.636 g, 6.42 mmol), acetone
+
−
(20 mL), and TMEDA (1.20 mL, 0.931 g, 8.01 mmol) with stirring. Then wet n-Bu N F (1.0 M
4
in THF, 5 wt% water, 0.40 mL, 0.40 mmol) was added to the three-neck flask with stirring. After
20 min (TLC, silica gel, 1:9 v/v CH Cl /hexanes, showed no remaining educt), Me SiCl (0.508
2
2
3
[5b,7]
mL, 4.02 mmol) was added. After 5 min, HC TES (3.30 g, 20.08 mmol)
was added, and O
4
2
was bubbled through the mixture. The CuCl/TMEDA suspension (20 mL) was added with stirring.
After 1 h at  °C, hexanes (100 mL) were added. The resulting dark green suspension was filtered
through a silica gel plug (5  7 cm, packed in 1:1 v/v acetone/hexanes), which was rinsed (1:1 v/v
acetone/hexanes) until the filtrate became colorless. The solvents were removed from the filtrate
by rotary evaporation at < 20 °C. The brown residue was chromatographed on a silica gel column
(4.5 × 30 cm, packed in hexanes, eluted with hexanes, then with a CH Cl gradient until 3:1 v/v
2
2
CH Cl /hexanes). The solvents were removed from the product containing fractions by rotary ev-
2
2
aporation at < 20 °C to give, in order of elution, (1) TESC TES as a yellow oil which was dis-
8
solved in a minimum of HCl
/EtOH (1:100 v/v) and kept in the freezer (−35 °C) to form a pale
conc
yellow solid (2.045 g, 6.261 mmol, ca. 65%), and (2) PtC TES as a yellow-orange solid (0.688
10
-23-
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10.1002/chem.202101725
Chemistry - A European Journal
g, 0.570 mmol, 71%), which slightly darkened at 105 °C and turned black at 130 °C (open capil-
[39]
lary). DSC (T /T /T /T /T ):
exotherm, 120.8/131.6/148.9/159.0/164.1 °C. TGA: onset of mass
i
e
p
c
f
loss 197.4 °C (T ). Anal. Calcd for C H F P PtSi: C, 63.73; H, 4.76. Found: C, 64.09; H, 5.11.
i
64 57 5 2
No efforts were made to isolate PtC Pt, the formation of which was confirmed by TLC.
12
1
[40]
NMR (/ppm, CDCl ): H (500 MHz, cryoprobe)
7.48−7.44 (m, 12H, o to P), 7.12 (d,
3
3
3
J
= 7.8 Hz, 12H, m to P), 2.37 (s, 18H, CH p to P), 0.98 (t, J = 7.9 Hz, 9H, CH CH ),
HH
3
HH
2
3
3
13
1
[42,43,44a]
1
0.62 (q, J = 7.9 Hz, 6H, SiCH ); C{ H} (126 MHz, cryoprobe)
146.0 (dd, J
=
HH
2
CF
2
226 Hz, J = 21.4 Hz, o to Pt), 141.2 (s, p to P), 138.3−135.4 (2 m, p and m to Pt), 134.4 (virtual
CF
2
3
1
t, J = 6.4 Hz, o to P), 128.9 (virtual t, J = 5.5 Hz, m to P), 127.1 (virtual t, J = 30.4 Hz,
CP
CP
CP
2
[45]
1
i to P), 108.2 (br s, PtCC), 95.2 (s, J = 262 Hz,
PtCC), 89.8 (s, CCSi), 84.9 (s, J
=
CPt
CSi
[45]
73.1 Hz,
CCSi), 66.8, 65.2, 63.3, 60.5, 59.7, 56.7 (6 s, PtCC(CC) ), 21.5 (s, CH p to P),
3 3
1
[45]
31
1
1
7.5 (s, CH CH ), 4.3 (s, J = 56.7 Hz,
SiCH ); P{ H} (202 MHz) 18.00 (s, J = 2610
2 PPt
2
3
CSi
[45] 19
1
3
[45]
Hz);
F{ H} (470 MHz) −115.86 to −116.54 (m, J = 291 Hz,
2F, o to Pt), −163.46 to
FPt
3
−163.58 (m, 2F, m to Pt), −163.83 (t, J = 18.8 Hz, 1F, p to Pt). Additional data: see Table 2 and
FF
the Supporting Information.
trans-(C F )(p-tol P) Pt(CC) SiEt (PtC TES). A three-neck round bottom flask was
6 5
3
2
9
3
18
fitted with a gas dispersion tube, charged with PtC TES (0.390 g, 0.311 mmol) and THF (150
14
mL), and cooled to − °C. A Schlenk flask was charged with CuCl (0.123 g, 1.24 mmol), acetone
+
−
(15 mL), and TMEDA (0.234 mL, 0.182 g, 1.57 mmol) with stirring. Then wet n-Bu N F (1.0
4
M in THF, 5 wt% water, 0.16 mL, 0.16 mmol) was added to the three-neck flask with stirring.
After 10 min (TLC, silica gel, 1:9 v/v CH Cl /hexanes, showed no remaining educt), Me SiCl
2
2
3
[5b,7]
(0.20 mL, 1.58 mmol) was added. After 10 min, HC TES (1.28 g, 7.79 mmol)
was added
4
and O was bubbled through the mixture. The CuCl/TMEDA suspension (15 mL) was added with
2
stirring. After 5 min, the cooling bath was removed. After 55 min, hexanes (100 mL) were added.
The resulting dark brown suspension was filtered through a pad of silica gel (5  7 cm, packed in
hexanes), which was rinsed (1:1 v/v acetone/hexanes) until the filtrate became colorless. The solv-
ents were removed from the filtrate by rotary evaporation at < 10 °C. The red brown residue was
-24-
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10.1002/chem.202101725
Chemistry - A European Journal
chromatographed on a silica gel column (4.5 × 30 cm, packed in hexanes, eluted with hexanes,
then with a CH Cl gradient until 3:1 v/v CH Cl /hexanes). The solvents were removed from the
2
2
2
2
product containing fractions by rotary evaporation at < 10 °C to give a dark orange oil. The add-
ition of cold MeOH afforded a precipitate that was collected by filtration and dried by oil pump
vacuum to give PtC TES as a dark orange powder (0.110 g, 0.084 mmol, 27%), which slightly
18
[39]
darkened at 55 °C and turned black at 85 °C (open capillary). DSC (T /T /T /T /T ):
endo-
i
e
p
c
f
therm, 56/58/63/67/69 °C; exotherm: 89/108/123/135/146 °C. TGA: onset of mass loss, 160 °C
(T ). Anal. Calcd for C H F P PtSi: C, 66.40; H, 4.41. Found: C, 66.13; H, 4.50.
i
72 57 5 2
1
[41]
NMR (/ppm, CDCl ): H (500 MHz, cryoprobe)
7.46−7.42 (m, 12H, o to P), 7.12 (d,
3
3
3
J
= 7.8 Hz, 12H, m to P), 2.37 (s, 18H, CH p to P), 1.00 (t, J = 7.9 Hz, 9H, CH CH ),
HH
3
HH
2
3
3
13
1
[42,43,44b]
1
0.65 (q, J = 7.9 Hz, 6H, SiCH ); C{ H} (126 MHz, cryoprobe)
146.0 (dd, J
=
HH
2
CF
2
226 Hz, J = 22.7 Hz, o to Pt), 141.3 (s, p to P), 138.3−135.4 (2 m, p and m to Pt), 134.3 (virtual
CF
2
3
1
t, J = 6.4 Hz, o to P), 128.9 (virtual t, J = 5.6 Hz, m to P), 126.9 (virtual t, J = 30.4 Hz,
CP
CP
CP
i to P), 111.0 (m, PtCC), 94.9 (s, PtCC), 88.9 (s, CCSi), 87.9 (s, CCSi), 67.6, 66.4, 65.0, 64.1,
63.4, 62.9, 62.8, 62.4, 61.9, 61.7, 60.7, 59.7, 56.7 (13 s, PtCC(CC) ), 21.5 (s, CH p to P), 7.4
7
3
1
[45]
31
1
1
(s, CH CH ), 4.2 (s, J
= 56.7 Hz,
SiCH ); P{ H} (202 MHz) 18.04 (s, J = 2602
2 PPt
2
3
CSi
[45] 19
1
3
[45]
Hz);
F{ H} (470 MHz) −115.83 to −116.52 (m, J = 296 Hz,
2F, o to Pt), −163.29 to
FPt
3
−163.42 (m, 2F, m to Pt), −163.57 (t, J = 19.2 Hz, 1F, p to Pt). Additional data: see Table 2 and
FF
the Supporting Information.
trans-(C F )((p-tol) P) Pt(CC) C=CHN(CH C H )N=N (PtC HN Bz). A.
A
6 5
3
2
2
2
6
5
6
3
[5a]
Schlenk flask was sequentially charged with PtC TES (0.300 g, 0.260 mmol),
THF (5 mL)
6
+
–
and wet n-Bu N F (1.0 M in THF, 5 wt % water, 0.050 mL, 0.050 mmol). The mixture was
4
stirred (0.5 h), and Me SiCl (0.020 mL, 0.16 mmol) was added. Then DMF (10 mL), benzyl azide
3
(0.032 mL, 0.034 g, 0.260 mmol), CuSO ·5H O (0.100 g, 0.403 mmol), ascorbic acid (0.100 g,
4
2
0.568 mmol), and water (2 mL) were added with stirring. After 16 h, the solvents were removed
by oil pump vacuum. Water was added and the sample was extracted with CH Cl (3  50 mL).
2
2
The combined extracts were dried (MgSO ) and concentrated. The residue was chromatographed
4
-25-
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10.1002/chem.202101725
Chemistry - A European Journal
on a silica gel column using CH Cl . The solvent was removed from the product containing frac-
2
2
tions by oil pump vacuum to give PtC HN Bz as an off-white powder (0.215 g, 0.183 mmol,
6
3
[5a]
70%). B. A Schlenk flask was charged with PtC TES (0.100 g, 0.0863 mmol)
and THF (5
6
mL). Benzyl azide (0.026 M in DMF, 7.0 mL, 0.18 mmol), CuSO ·5H O (0.40 M in water, 0.50
4
2
mL, 0.20 mmol), and ascorbic acid (0.57 M in water, 0.50 mL, 0.28 mmol) were added with stir-
+
−
ring. Then wet n-Bu N F (1.0 M in THF, 5 wt% water, 0.10 mL, 0.10 mmol) was added. After
4
16 h (TLC showed no remaining educt), the solvents were removed by oil pump vacuum. Water
(10 mL) was added and the sample was extracted with CH Cl (3  50 mL). The combined extracts
2
2
were dried (MgSO ) and the solvent was removed by rotary evaporation and oil pump vacuum.
4
The residue was chromatographed on a silica gel column (1.5  16 cm, eluted with CH Cl ). The
2
2
solvent was removed from the product containing fractions by rotary evaporation and oil pump
vacuum to give PtC HN Bz as a white powder (0.063 g, 0.054 mmol, 62%), which slightly dark-
6
3
ened at 180 °C, turned black at 257 °C, and liquefied at 260 °C (open capillary). Calcd for C H -
61 50
F N P Pt: C, 62.24; H, 4.28; N, 3.57; found: C, 62.20; H, 4.19; N, 3.52.
5
3 2
1
[41]
NMR (/ppm CDCl ): H (500 MHz)
7.54−7.51 (m, 12H, o to P), 7.29−7.28 (m, 3H,
3
m and p to CH ), 7.12−7.10 (m, 15H, m to P, CH and o to CH ), 5.29 (s, 2H, CH ), 2.34 (s, 18H,
2
2
2
13
1
[42,43,44c]
1
2
CH ); C{ H} (126 MHz)
145.8 (dd, J = 226 Hz, J = 20.2 Hz, o to Pt), 140.9 (s,
CF CF
3
p to P), 138.0−135.3 (2 m, p and m to Pt), 134.5, 132.4 (2 s, i to CH or CCC=CH; see also Table
2
2
3
1), 134.37 (virtual t, J = 6.4 Hz, o to P), 129.1, 128.0 (2 s, o or m to CH ), 128.7 (virtual t, J
CP
CP
2
1
= 5.6 Hz, m to P), 127.4 (virtual t, J = 30.2 Hz, i to P), 125.6 (s, CCC=CH), 106.5 (br s,
CP
2
[45]
4
PtCC), 95.1 (s, J = 269 Hz,
PtCC), 82.0 (t, J = 2.5 Hz, PtCCCC), 58.9 (s, PtCC-
CP
CPt
31
1
1
[45]
CC), 54.0 (s, CH ), 21.4 (s, CH ); P{ H} (202 MHz) 17.96 (s, J = 2653 Hz).
Additional
2
3
PPt
data: see Tables 2 and 3 and the Supporting Information.
trans-(C F )((p-tol) P) Pt(CC) C=CHN(CH C H )N=N (PtC HN Bz). A.
A
6 5
3
2
7
2
6
5
16
3
Schlenk flask was charged with PtC TES (0.100 g, 0.078 mmol) and THF (10 mL) and cooled
16
to 0 °C. Benzyl azide (0.0263 M in DMF, 4.5 mL, 0.12 mmol), CuSO ·5H O (0.401 M in water,
4
2
0.35 mL, 0.14 mmol), and ascorbic acid (0.568 M in water, 0.28 mL, 0.16 mmol) were added with
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10.1002/chem.202101725
Chemistry - A European Journal
stirring. After 5 min, wet n-Bu4N+ F− (1.0 M in THF, 5 wt% water, 0.15 mL, 0.15 mmol) was
added dropwise. The deep red solution slowly gave a brown precipitate. After 3 h (TLC showed
no remaining educt), the solvents were removed by oil pump vacuum. Water (10 mL) was added
and the sample was extracted with CH2Cl2 (3 × 50 mL). The combined extracts were dried (Mg-
SO ) and the solvent was removed by oil pump vacuum. The residue was chromatographed on a
4
silica gel column (2.5 × 30 cm, eluted with 1:1 v/v CH Cl /hexanes). The solvents were removed
2 2
from the product containing fractions by oil pump vacuum to give PtC HN Bz as a red powder
16
3
(0.055 g, 0.042 mmol, 54%). B. A Schlenk flask was charged with PtC TIPS (0.100 g, 0.076
16
mmol) and THF (10 mL) and cooled to  °C. Benzyl azide (0.024 M in DMF, 5.0 mL, 0.120
mmol), CuSO ·5H O (0.203 M in water, 1.0 mL, 0.20 mmol), and ascorbic acid (0.227 M in water,
4
2
+
−
1.0 mL, 0.227 mmol) were added with stirring. Then wet n-Bu N F (1.0 M in THF, 5 wt% water,
4
0.15 mL, 0.15 mmol) was added. The dark red mixture was stirred at  °C for 3 h. The THF was
removed by rotary evaporation. Water (50 mL) was added to the brown sample, and the mixture
was extracted with CH Cl (3 × 100 mL). The combined extracts were dried (MgSO ), and the
2
2
4
solvent was removed by rotary evaporation at < 20 °C. The dark red residue was chromatographed
on a silica gel column (30 × 4.5 cm, packed in CH Cl /hexanes 1:4 v/v, eluted with a CH Cl
2
2
2
2
gradient until 1:1 v/v CH Cl /hexanes). The solvents were removed from the product-containing
2
2
fractions by rotary evaporation at 25 °C to give PtC HN Bz as a dark orange solid. (0.064 g,
16
3
0.049 mmol, 64%), which slightly darkened at 62 °C and turned black at 99 °C (open capillary).
Anal. Calcd for C H F N P Pt: C, 65.74; H, 3.89; N, 3.24. Found: C, 65.86; H, 4.00; N, 3.22.
71 50 5 3 2
1
[41]
NMR (/ppm, CDCl ): H (500 MHz, cryoprobe)
7.64 (s, 1H, CH), 7.46−7.42 (m, 12H,
3
o to P), 7.39−7.38 (2 overlapping m, 3H, m and p to CH ), 7.27−7.25 (m, 2H, o to CH ) 7.12 (d,
2
2
3
13
1
J
= 7.8 Hz, 12H, m to P), 5.52 (s, 2H, CH ), 2.36 (s, 18H, CH ); C{ H} (126 MHz, cryo-
2 3
HH
[42,43,44b]
1
2
probe)
146.0 (dd, J = 225.0 Hz, J = 21.4 Hz, o to Pt), 141.3 (s, p to P), 138.2−135.4
CF CF
2
(2 m, p and m to Pt), 134.3 (virtual t, J = 6.3 Hz, o to P), 133.7, 129.54 (2 s, i to CH or
CP
2
CCC=CH; see also Table 1), 129.49, 128.4 (2 s, o or m to CH ), 129.4 (s, p to CH ), 128.9 (virtual
2
2
3
1
t, J = 5.6 Hz, m to P), 128.8 (s, CCC=CH), 127.0 (virtual t, J = 30.4 Hz, i to P), 110.6 (m,
CP
CP
-27-
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10.1002/chem.202101725
Chemistry - A European Journal
PtCC), 95.0 (s, PtCC), 78.3, 69.1, 67.8, 66.6, 66.4, 65.9, 65.6, 61.2 60.5, 59.6, 56.6 (11 s, Pt-
[44b]
31
1
1
[45]
CC(CC) ),
54.7 (s, CH ), 21.5 (s, CH ); P{ H} (202 MHz) 18.03 (s, J = 2596 Hz);
2 3 PPt
6
19
1
3
[45]
F{ H} (470 MHz) −115.84 to −116.53 (m, J = 296 Hz,
2F, o to Pt), −163.33 to −163.46
FPt
3
(m, 2F, m to Pt), −163.63 (t, J = 19.4 Hz, 1F, p to Pt). Additional data: see Tables 2 and 3 and
FF
the Supporting Information
Accession Codes. CCDC 2078980 (PtC TES), 2078981 (PtC TES), 2078982 (PtC TES),
10
12
14
2078983 (PtC TES), 2078984 (PtC TES(CH Cl ) ), 2078985 (PtC TES(CH Cl )),
16
18
2
2 0.74
20
2
2
2078986 (PtC TES(CH Cl ) ), 20078987 (PtC TIPS(CH Cl ) ), 2078988 (PtC TIPS),
20
2
2 0.5
12
2
2 0.5
14
2078989 (PtC TIPS), 932391 (PtC HN Bz), 932392 (PtC HN Bz(CH Cl ) ), 2078990
16
8
3
10
3
2
2 0.8
(PtC HN Bz(C H ) ), 2078991 (PtC HN Bz), 2078992 (PtC HN Bz(C H ) ),
12
3
6
14 0.5
14
3
16
3
6
14 2
[46]
2078993 (PtC HN Bz) contain the supplementary crystallographic data for this paper.
These
18
3
data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing
data_request@ccdc.cam.ac.uk, or by contacting The Cambridge Crystallographic Data Centre, 12
Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

ORCID
Hashem Amini: 0000-0002-9921-9816
John A. Gladysz: 0000-0002-7012-4872
Notes
The authors declare no competing financial interest.
Acknowledgements
The authors thank the US National Science Foundation (NSF; CHE-1566601, CHE-
1900549) for support, and Ms. Brenna Collins and Mr. Sourajit Dey Baksi for helping to stockpile
building blocks.
Key Words
alkyne cross-coupling, click reaction, crystal structures, platinum, polyyne, protodesilylation
.
-28-
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-29-
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