Hydroxide-, amide-, and sulfhydrylrhenium(I) tris(alkyne) complexes. Rearrangements to rhenium(III) bis(alkvne) oxo and nitrido compounds

Article abstract of DOI:10.1021/om9704814

The rhenium hydroxide and amide complexes Re(OH)(EtC≡CEt)₃ (3) and Re(NH₂)-(EtC≡CEt)S (10) have been prepared by reaction of the related aquo and ammine complexes with KOH and NaNH₂, respectively. The sulfhydryl compound Re(SH)(EtC≡CEt)₃ (13) is formed from Re(OSO₂CF₃)(EtC≡CEt)₃ and NaSH. Compound 3 spontaneously rearranges to the oxo-hydride complex Re(O)H(EtC≡CEt)₂ (4), and EtC≡CEt in a first-order process (k = (5.6 ± 1.2) × 10^-6 s^-1 at 294 K). There is a primary isotope effect (k_OH/k_OD = 5 ± 1), and the rearrangement is unaffected by the presence of 1 M 3-hexyne. These data rule out a mechanism involving initial ligand loss followed by rearrangement. Instead, hydrogen migration from oxygen to rhenium occurs in the coordinatively saturated tris(alkyne) species 3, either synchronously with or prior to the loss of alkyne. Rearrangement is catalyzed by potassium alkoxides, apparently via deprotonation of 3 and concomitant loss of EtC≡CEt to the oxo anion (EtC≡CEt)₂ReO^- (5), which is reprotonated by ROH. Surprisingly, isolated samples of 5 are not catalysts, apparently due to its slow proton transfer reactions. The amide complex 10 rearranges to the unusual μ-nitrido complex (EtC≡CEt)₃Re-N≡Re(H)-(EtC≡CEt)₂ (11), which has been characterized spectroscopically. This reaction is similar to that of the hydroxide 3 in that a hydrogen moves from N or O to the rhenium center, with oxidation of the metal. The mechanism of rearrangement is quite different, however, as added alkynes strongly inhibit conversion of 10 to 11, indicating initial 3-hexyne dissociation from 10. No rearrangement has been observed for the sulfhydryl compound 13, which decomposes at 150 °C.

Full text of DOI:10.1021/om9704814

5342
Organometallics 1997, 16, 5342-5353
Hyd r oxid e-, Am id e-, a n d Su lfh yd r ylr h en iu m (I)
Tr is(a lk yn e) Com p lexes. Rea r r a n gem en ts to
Rh en iu m (III) Bis(a lk yn e) Oxo a n d Nitr id o Com p ou n d s1
Sam K. Tahmassebi, W. Stephen McNeil, and J ames M. Mayer*
Department of Chemistry, Box 351700, University of Washington,
Seattle, Washington 98195-1700
Received J une 9, 1997X
The rhenium hydroxide and amide complexes Re(OH)(EtCtCEt)3 (3) and Re(NH2)-
(EtCtCEt)3 (10) have been prepared by reaction of the related aquo and ammine complexes
with KOH and NaNH2, respectively. The sulfhydryl compound Re(SH)(EtCtCEt)3 (13) is
formed from Re(OSO2CF3)(EtCtCEt)3 and NaSH. Compound 3 spontaneously rearranges
to the oxo-hydride complex Re(O)H(EtCtCEt)2 (4), and EtCtCEt in a first-order process
(k ) (5.6 ( 1.2) × 10-6 s-1 at 294 K). There is a primary isotope effect (kOH/kOD ) 5 ( 1),
and the rearrangement is unaffected by the presence of 1 M 3-hexyne. These data rule out
a mechanism involving initial ligand loss followed by rearrangement. Instead, hydrogen
migration from oxygen to rhenium occurs in the coordinatively saturated tris(alkyne) species
3, either synchronously with or prior to the loss of alkyne. Rearrangement is catalyzed by
potassium alkoxides, apparently via deprotonation of 3 and concomitant loss of EtCtCEt
to the oxo anion (EtCtCEt)2ReO- (5), which is reprotonated by ROH. Surprisingly, isolated
samples of 5 are not catalysts, apparently due to its slow proton transfer reactions. The
amide complex 10 rearranges to the unusual µ-nitrido complex (EtCtCEt)3Re-NtRe(H)-
(EtCtCEt)2 (11), which has been characterized spectroscopically. This reaction is similar
to that of the hydroxide 3 in that a hydrogen moves from N or O to the rhenium center,
with oxidation of the metal. The mechanism of rearrangement is quite different, however,
as added alkynes strongly inhibit conversion of 10 to 11, indicating initial 3-hexyne
dissociation from 10. No rearrangement has been observed for the sulfhydryl compound
13, which decomposes at 150 °C.
In tr od u ction
known alkoxide, oxo-alkyl, and related compounds.5-9
In such transformations, the metal undergoes a two-
electron change in the formal oxidation state and the
group R formally converts from R+ to R-.
[1,2]- or R-migration of a hydrogen or a hydrocarbyl
group between a metal center and a ligand is a funda-
mental organometallic transformation (eq 1).2 It inter-
The most famous invocation of this rearrangement is
the redox step in the Sharpless mechanism for oxidation
of alkenes by OsO4 and related oxidants, the transfor-
mation of an oxametallacyclobutane to a diolate ligand.6
There are only two clear examples of an alkoxide/oxo-
alkyl interconversion. A Cp*2TaOCH3 intermediate
converts compounds of quite different structure and
reactivity. It is facile and common when E is a Fischer
carbene ligand2 and has been reported in some Schrock
alkylidene and alkylidyne complexes.2,3 There are
numerous related [1,2]-migrations in organic chemistry,
including Wagner-Meerwein shifts, rearrangements of
carbenes, and Wittig, Wolff, and Stevens rearrange-
ments.4 But [1,2]-migrations involving a metal and an
electronegative group E, such as an oxo, a sulfido, or
an imido group, are rare despite the large number of
(5) Brown, S. N.; Mayer, J . M. J . Am. Chem. Soc. 1996, 118, 12119-
12133.
(6) (a) Sharpless, K. B.; Teranishi, A. Y.; Ba¨ckvall, J .-E. J . Am.
Chem. Soc. 1977, 99, 3120. (b) Hentges, S. G.; Sharpless, K. B. J . Am.
Chem. Soc. 1980, 102, 4263. (c) Nelson, D. W.; Gypser, A.; Ho, P. T.;
Kolb, H. C.; Kondo, T.; Kwong, H.-L.; McGrath, D. V.; Rubin, A. E.;
Norrby, P.-O.; Gable, K. P.; Sharpless, K. B. J . Am. Chem. Soc. 1997,
119, 1840-1858. (d) Norrby, P.-O.; Becker, H.; Sharpless, K. B. J . Am.
Chem. Soc. 1996, 118, 35. (e) Gable, K. P.; J uliette, J . J . J . J . Am.
Chem. Soc. 1996, 118, 2625-2633. (f) J ørgensen, K. A.; Schiøtt, B.
Chem. Rev. 1990, 90, 1483-1506.
(7) (a) van Asselt, A.; Burger, B. J .; Gibson, V. C.; Bercaw, J . E. J .
Am. Chem. Soc. 1986, 108, 5347. (b) Parkin, G.; Bunel, E.; Burger, B.
J .; Trimmer, M. S.; van Asselt, A.; Bercaw, J . E. J . Mol. Catal. 1987,
41, 21. (c) Nelson, J . E.; Parkin, G.; Bercaw, J . E. Organometallics 1992,
11, 2181.
X Abstract published in Advance ACS Abstracts, November 1, 1997.
(1) Low-Valent Rhenium-Oxo Compounds. 16. Part 15: ref 29.
(2) (a) Collman, J . P.; Hegedus, L. S.; Norton, J . R.; Finke, R. G.
Principles and Applications of Organotransition Metal Chemistry;
University Science Books: Mill Valley, CA, 1987. (b) Crabtree, R. H.
The Organometallic Chemistry of the Transition Metals, 2nd ed.; Wiley-
Interscience: New York, 1994.
(3) To our knowledge, the only example of alkyl migration to a
Schrock carbene is apparently in the rearrangement of Cp2Ta(CHMe)-
CH3 to Cp2Ta(CH2dCHMe)H, see: Sharp, P. R.; Schrock, R. R. J .
Organomet. Chem. 1979, 171, 43-51.
(4) March, J . Advanced Organic Chemistry, 4th ed.; Wiley-Inter-
science: New York, 1992. Harwood, L. M. Polar Rearrangements;
Oxford: New York, 1992.
(8) For instance, see references in ref 6 and (a) Nugent, W. A.;
Harlow, R. L. J . Am. Chem. Soc. 1980, 102, 1759. (b) Vivanco, M.; Ruiz,
J .; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C. Organometallics 1993, 12,
1802-1810. (c) Matsunaga, P. T.; Mauropoulos, J . C.; Hillhouse, G. L.
Organometallics 1995, 14, 175. (d) Go´mez, M.; Go´mez-Sal, P.; J ime´nez,
G.; Mart´ın, A.; Royo, P.; Sa´nchez-Nieves, J . Organometallics 1996, 15,
3579-3587.
(9) Tahmassebi, S. K.; Conry, R. R.; Mayer, J . M. J . Am. Chem. Soc.
1993, 115, 7553.
S0276-7333(97)00481-0 CCC: $14.00 © 1997 American Chemical Society

Rhenium(I) Tris(alkyne) Complexes
Organometallics, Vol. 16, No. 24, 1997 5343
rearranges to the isomeric oxo-methyl complex, Cp*2-
Ta(O)CH3 (Cp* ) η5-C5Me5).7 Labeling studies provide
strong evidence for the related hydroxide-to-oxo hydride
rearrangement, and analogous chemistry with nitrogen
and sulfur ligands was described. The cationic rhenium
dioxo-phenyl complex TpReO2Ph+OTf- has been found
to rearrange below room temperature to a phenoxide
complex.5 Related interconversions have been discussed
in a number of systems,8 but without direct observation
of key species. To give two examples, treatment of a
chromium tert-butylimido complex with diphenylzinc
gives PhNHtBu upon hydrolysis, suggesting an aryl-to-
nitrogen migration,8a and sulfur insertion into a vana-
dium-iminoacyl linkage has been suggested to occur
via eq 1, with E ) S.8b
We have communicated the synthesis of the rhenium-
(I) tris(3-hexyne) hydroxide complex 3 and its rear-
rangement to the rhenium(III) bis(3-hexyne) oxo-
hydride compound (4; eq 2).9 This contrasts with the
lack of interconversion of isolated methoxide and oxo-
methyl complexes in this system (eq 3).10 Here we
F igu r e 1. ORTEP diagram of the X-ray crystal structure
of Re(OTf)(EtCtCEt)3 (2).
Ta ble 1. Cr ysta llogr a p h ic Da ta
Re(OTf)(EtCtCEt)3 Re(OH)(EtCtCEt)3
(2)
(3)
empirical formula
fw
C19H30F3O3ReS
581.7
C18H31ORe
449.6
cryst syst
space group
a, Å
b, Å
c, Å
monoclinic
P21/n
8.410(2)
monoclinic
P21/m
report a more complete study of the hydroxide rear-
rangement along with a comparative study of the
reactions of analogous tris(alkyne)-amido and -sulf-
hydryl complexes.
7.734(2)
13.123(4)
9.162(5)
101.65(3)
910.7(6)
1.640
Mo KR (λ )
0.710 73 Å)
2 e 2θ e 45
1257
939 (Rint ) 4.25%)
889 (F > 4σF)
66.67
8.35
8.92
19.450(4)
14.660(3)
102.55(3)
2347.4(12)
1.646
Mo KR (λ )
0.710 73 Å)
2 e 2θ e 50
4684
4108 (Rint ) 2.53%)
2313 (F > 4σF)
53.03
4.97
6.76
â, deg
V, Å3
Dcalcd, g/cm3
radiation
Resu lts
2θ range, deg
no. of reflns colld
no. of indep reflns
no. of obsd reflns
µ (Mo KR), cm-1
R, %
Rh en iu m (I) Tr is(3-h exyn e) Hyd r oxid e Com p lex
3. Rhenium(I) tris(alkyne) complexes such as Re(I)-
(EtCtCEt)3 (1) are prepared by reduction of rhenium-
(III) oxo-bis(alkyne) compounds Re(O)I(RCtCR)2.10,11
As an improvement over the reported procedure, sodium
reduction followed by Me3SiI, the oxygen atom can,
instead, be cleanly removed with PMePh2 in the pres-
ence of added alkyne (eq 4). PPh3 is not a strong enough
Rw, %
GOF
1.39
1.52
16.8:1
data-to-parameter ratio 12.1:1
(2) (OTf ) triflate, O3SCF3).10 The X-ray crystal struc-
ture of 2 (Figure 1, Table 1) shows isolated molecules
which exhibit disorder in some of the alkyne ethyl
groups and in the triflate CF3 group (see Experimental
Section). The bond lengths and angles in 2 are dis-
cussed below. The triflate ligand is readily displaced
by anionic and neutral ligands.10
Addition of water to a benzene solution of 2 generates
an equilibrium amount of the aquo complex [Re(H2O)-
(EtCtCEt)3]OTf, which has not been isolated. Treat-
ment of this equilibrium mixture with solid KOH
quantitatively gives the hydroxide complex Re(OH)-
(EtCtCEt)3 (3), as monitored by 1H NMR (eq 5).
Complex 3 is quite soluble in organic solvents and also
in the oxo-hydride complex, Re(O)H(EtCtCEt)2 (4), an
oil which forms during workup (vide infra). Thus,
reductant, and reaction with PMe3 apparently leads to
alkyne displacement as well as reduction.12 AgOTf
converts 1 into the triflate complex, Re(OTf)(EtCtCEt)3
(10) Conry, R. R.; Mayer, J . M. Organometallics 1993, 12, 3179.
(11) Conry, R. R.; Mayer, J . M. Organometallics 1991, 10, 3160.
(12) Mayer, J . M.; Thorn, D. L.; Tulip, T. H. J . Am. Chem. Soc. 1985,
107, 7454.

5344 Organometallics, Vol. 16, No. 24, 1997
Tahmassebi et al.
Ta ble 3. Selected Bon d An gles (d eg) for
Re(OH)(EtCtCEt)3 (3), Re(OTf)(EtCtCEt)3 (2), a n d
Re(OSiMe3)(MeCtCMe)3
anglea
Re(OH)
Re(OTf)
Re(OSiMe3)b
O-Re-C3
125.6(5)
122.0(9)
NAc
88.1(5)
84.0(9)
NAc
37.7(6)
38.0(10)
NAc
127.4(5)
127.7(6)
121.5(5)
90.4(5)
91.5(6)
84.9(5)
37.1(6)
36.4(7)
36.6(7)
89.9(7)
89.7(7)
89.0(6)
119.7(6)
122.6(6)
117.6(6)
135.0(6)e
124.8(4)
124.3(4)
125.6(4)
88.7(5)
85.3(4)
88.5(4)
36.1(4)
39.1(4)
37.3(4)
91.2(4)
88.0(5)
92.2(4)
120.5(4)
120.3(4)
118.6(5)
167.2(6)f
O-Re-C9
O-Re-C15
O-Re-C4
O-Re-C10
O-Re-C16
C3-Re-C4
C9-Re-C10
C15-Re-C16
C3-Re-C9
C9-Re-C15
C3-Re-C15
C4-Re-C10
C10-Re-C16
C4-Re-C16
Re-O-X
90.4(7)
NAc
NAc
119.7(6)
NAc
NAc
NAd
F igu r e 2. ORTEP diagram of the X-ray crystal structure
of Re(OH)(EtCtCEt)3 (3).
a
Numbering scheme refers to the structure of 2 (Figure 1).
Data from ref 10. c Because of a crystallographic mirror plane, 3
b
Ta ble 2. Selected Bon d Len gth s (Å) for
Re(OH)(EtCtCEt)3 (3), Re(OTf)(EtCtCEt)3 (2), a n d
Re(OSiMe3)(MeCtCMe)3
has only two unique alkyne ligands and, thus, has no C15 or C16.
d
The hydrogen atom of the hydroxide group in 3 was not located.
e X ) S. f X ) Si.
bonda
Re(OH)
Re(OTf)
Re(OSiMe3)c
(16), and 2.027 (8) Å for 2, 3, and the siloxideswith the
weakly bound triflate having the longest bond. The
distance between two neighboring oxygen atoms in solid
3 is about 8 Å, ruling out any hydrogen bonding between
hydroxide ligands. Consistent with this conclusion, a
sharp O-H stretch is observed at 3630 cm-1 in a Nujol
mull of 3 (νOD, 2677; calcd, 2633 cm-1), typical of metal
hydroxide complexes.14 A band at the same frequency
is observed in benzene solution, indicating the absence
of hydrogen bonding in solution as well.
1H NMR spectra of 3 at -66 °C in C7D8 show two
triplets for the methyl groups and two simple quartets
for the methylene protons, indicating C3v symmetry. 1H
NMR spectra at 27 °C, however, show a single methyl
triplet and a broad peak for the methylene hydrogens.
Resonances for 3-hexyne added to a solution of 3 remain
sharp at these temperatures, so ligand exchange is not
responsible for the coalescence. The fluxional process
Re-O1
Re-C4
2.124(16)
2.006(16)
1.983(30)
NAb
2.057(16)
1.955(21)
NAb
1.312(21)
1.282(36)
NAb
2.201(10)
2.009(14)
2.002(17)
1.981(15)
1.993(15)
1.992(16)
2.002(14)
1.273(21)
1.246(26)
1.251(23)
2.027(8)
2.028(11)
2.004(10)
2.023(10)
2.005(11)
2.066(11)
2.019(10)
1.251(15)
1.363(15)
1.292(14)
Re-C10
Re-C16
Re-C3
Re-C9
Re-C15
C3-C4
C9-C10
C15-C16
a
The numbering scheme refers to the structure of 2 (Figure 1).
Complex 3 has only two unique alkyne ligands due to its site
b
symmetry. c Data from ref 10.
is most likely rotation of the alkyne ligand(s), as
10,15
suggested for similar ReX(RCtCR)3
and W(L)-
(RCtCR)3 compounds.13 The coalescence temperature
is found to be 295 K for the methylene protons, indicat-
ing that ∆Gq
) 14.0 ( 0.2 kcal/mol. The 13C NMR
rotation
chemical shifts of the acetylenic carbons, 167.6 and
179.0 ppm at 240 K, are in the same range as for the
other tris(acetylene) complexes and are consistent with
the alkynes acting as 31/3 electron-donor ligands, as
predicted by symmetry arguments and the 18-electron
rule.16
isolated yields of 3 are only 35% after recrystallization
from pentane. Solid 3 is stable at -11 °C under inert
atmosphere for at least a few months.
Conversion of 3 to the oxo-hydride Re(O)H(EtCtCEt)2
(4)17 and 3-hexyne (eq 2) is complete after 5 days in
benzene solution at ambient temperatures and proceeds
The X-ray crystal structure of 3 (Figure 2, Table 1)
shows that the isolated molecules lie on a crystal-
lographic mirror plane which contains rhenium, oxygen,
and one alkyne ligand. The triflate (2), hydroxide (3),
and siloxide Re(OSiMe3)(MeCtCMe)310 complexes have
nearly identical capped trigonal prism coordination, as
is characteristic of ML(alkyne)3 compounds (Tables 2
and 3).13 The most notable difference between these
structures is the Re-O bond lengths2.201 (10), 2.124
1
with a mass balance of nearly 100% by H NMR. This
(14) (a) Imadea, M.; Nishihara, H.; Nakano, K.; Ichida, H.; Koba-
yashi, A.; Saito, T.; Sasaki, Y. Inorg. Chem. 1985, 24, 1246. (b) Milstein,
D.; Calabrese, J . C.; Williams, I. D. J . Am. Chem. Soc. 1986, 108, 6387.
(c) Chaudret, B. N.; Cole-Hamilton, D. J .; Nohr, R. S.; Wilkinson, G.
J . Chem. Soc., Dalton Trans. 1977, 1546. (d) Yoshida, T.; Okano, T.;
Otsuka, S. J . Chem. Soc., Dalton Trans. 1976, 993.
(15) Manion, A. B.; Erikson, T. K. G.; Spaltenstein, E.; Mayer, J .
M. Organometallics 1989, 8, 1871.
(16) (a) Templeton, J . L. Adv. Organomet. Chem. 1989, 29, 1-100.
(b) King, R. B. Inorg. Chem. 1968, 7, 1044.
(13) Wink, D. J .; Creagan, B. T. Organometallics 1990, 9, 328 and
references therein.
(17) Spaltenstein, E.; Erikson, T. K. G.; Critchlow, S. C.; Mayer, J .
M. J . Am. Chem. Soc. 1989, 111, 617.

Rhenium(I) Tris(alkyne) Complexes
Organometallics, Vol. 16, No. 24, 1997 5345
rearrangement occurs in the solid state and in a variety
of solvents; its kinetics and mechanism are discussed
below. Benzene solutions of 3 react rapidly with triflic
10
acid or HCl gas to give water and 2 or ReCl(EtCtCEt)3
(eq 6). Addition of NH3 or H2S forms the amide or
sulfhydryl complex (10, 13; vide infra). Reaction with
MeI gives H NMR signals attributable to the methanol
Complex 5 is readily protonated in acetonitrile by water,
alcohols, and other proton donors; the pKa of its conju-
gate acid 4 is estimated to be 33 ( 3 in MeCN.20
Rh en iu m (I) Tr is(3-h exyn e) Am in e a n d Am id o
Com p lexes. Ammonia, methylamine, and para-tolui-
dine displace the triflate ligand from 2 and form amine
complexes [Re(NH2R)(EtCtCEt)3]OTf (R ) H (6), Me
(7), C6H4Me (8); eq 9). Recrystallization from pentane
1
complex [Re(MeOH)(EtCtCEt)3]I, followed by conver-
sion to methanol and ReI(EtCtCEt)3 (1). This presum-
ably occurs through electrophilic attack of MeI on 3
followed by iodide displacement of methanol. Addition
of methanol to a benzene solution of 3 immediately
changes the 1H NMR to that expected for a nonfluxional
tris(3-hexyne) species. In the course of a few days, the
solution converts to the methoxide complex Re(OMe)-
(EtCtCEt)3 and water. No formation of the oxo-
hydride complex 4 is observed in the presence of MeOH.
Excess water also causes the 3-hexyne ligands of 3 to
become nonfluxional. The changes in the spectrum of
3 are apparently due to the formation of hydrogen bond-
(s).
Deprotonation of 3 by NaN(SiMe3)2 in acetonitrile
cleanly gives the known deep orange rhenium(I) oxo
anion (EtCtCEt)2Re(O)Na (5; eq 7).18 Addition of
gives 6-8 as analytically pure light gray solids in ca.
85% yield. They are indefinitely stable under inert
atmosphere but decompose upon exposure to air. Reac-
tion with aniline gives an equilibrium mixture contain-
ing [Re(NH2C6H5)(EtCtCEt)3]OTf (9), 2, and free aniline.
With p-nitroaniline, the equilibrium is so unfavorable
1
that no adduct can be seen in the H NMR spectrum.
The coordinating ability of the amines, thus, correlates
with their basicity, consistent with the observation of
an equilibrium with water as the ligand (eq 5).
The H and 13C NMR spectra of compounds 6-9 are
1
typical of ML(EtCtCEt)3 complexes, with separate
resonances for the proximal and distal ethyl groups,
nondiastereotopic methylene hydrogens, and acetylenic
13C chemical shifts in the range of 160-180 ppm.16 The
IR spectra of 6-8 show bands in the range of 3100-
3300 cm-1 for NH2 stretches and ca. 1600 cm-1 for NH2
bends. A strong peak at ∼1270 cm-1 is attributed to
the triflate counterion, consistent with its formulation
as an ionic triflate group.10,21 The 19F chemical shifts
in the vicinity of -2.3 ppm in C6D6 (vs CF3COOH) also
indicate that the triflate is ionic.22
KOMe, KOtBu, or KOPh to an acetonitrile solution of 3
causes an immediate color change from light yellow to
the orange color of 5, which then rapidly changes to dark
yellow, and H NMR spectra show the formation of 4.
The alkoxide salts are catalysts for the conversion of 3
to 4, apparently by the mechanism in eq 8.
The weaker bases triethylamine, pyridine, and potas-
sium p-nitrophenoxide do not deprotonate 3. With the
assumption that these kinetic observations reflect its
thermodynamic acidity, the pKa of 3 in acetonitrile is
between 20.7 and 27.2, the pKa’s of p-nitrophenol and
phenol in this solvent.19 It should be emphasized,
however, that deprotonation of 3 is not a simple or
reversible process, as removal of the acidic hydrogen is
accompanied by loss of an alkyne ligand (eq 7) and
reprotonation of 5 gives the rhenium hydride 4, not 3.
1
(20) (a) Complex 5-Na+ is completely protonated by H2O in MeCN
(pKa = 3020b) but 5-Na+ and 5-[Na(Krypotofix-222)]+ do not react with
MeCN solvent.11,18 Bases stronger than pKa ≈36 are reported to be
unstable in MeCN.20c These upper and lower bounds yield the
estimated pKa of 33 ( 3, ignoring counterion and other effects (e.g.,
Na+ may stabilize the OH- or OR- anions). (b) Barrette, W. C., J r.;
J ohnson, H. W., J r.; Sawyer, D. T. Anal. Chem. 1984, 56, 1890-1898.
(c) Kristja´nsdo´ttir, S. S.; Norton, J . R. In Transition Metal Hydrides:
Recent Advances in Theory and Experiment; Dedieu, A., Ed.; VCH:
New York 1991 (especially ref 25).
(18) Cundari, T. R.; Conry, R. R.; Spaltenstein, E.; Critchlow, S. C.;
Hall, K. A.; Tahmassebi, S. K.; Mayer, J . M. Organometallics 1994,
13, 322. The spectroscopic and structural properties of 5 do not vary
substantially with the cation, so we do not distinguish the different
salts here.
(19) Kolthoff, I. M.; Chantooni, M. K.; Bhowmik, S. J . Am. Chem.
Soc. 1968, 90, 23.
(21) Lawrance, G. A. Chem. Rev. 1986, 86, 17.
(22) In our rhenium systems, 19F chemical shifts for ionic triflates
in C6D6 are roughly -3 ppm (upfield of CF3COOH), whereas covalently
bound triflates appear closer to -1 ppm.5,10,21

5346 Organometallics, Vol. 16, No. 24, 1997
Tahmassebi et al.
1
The ammonia complex 6 is converted to the neutral
amido complex, Re(NH2)(EtCtCEt)3 (10), by NaNH2 or
NaH (eq 10). NaH must react by deprotonation, but
the H NMR by two clean quartets for the methylene
protons, while the bis(acetylene) fragment shows mul-
tiplets for the diastereotopic methylene hydrogens (as
found for all the rhenium(III) oxo-bis(acetylene) com-
pounds). The quartet and multiplet signals integrate
6:4, and this ratio does not change from one preparation
to another nor after sublimation, indicating they all
result from a single compound. The hydride ligand is
1
found in the H NMR as a singlet at 5.2 ppm (c.f., δ 6.0
for Re(O)H(EtCtCEt)2), and the Re-H stretch is as-
signed to a band in the IR spectrum at 1931 cm-1. Mass
spectra show a weak pattern at m/z 797 (M+) and a
stronger pattern at m/z 715 (M+ - EtCtCEt), which
shows the isotope pattern of a bimetallic rhenium
species. (M+ - EtCtCEt is invariably one of the largest
peaks in the MS of ReX(EtCtCEt)3 compounds.) Ini-
tially, the rearrangement of 10 to 11 is clean, exhibiting
a mass balance of close to 100% by NMR. But 11
decomposes slowly at room temperature to oily, NMR-
silent materials. This is one of the more unusual
methods of synthesis of a µ-nitrido bimetallic com-
pound.23
NaNH2 could react either by deprotonation or substitu-
tion; reaction of the aquo complex with NaOMe gives
both the hydroxide and methoxide complexes. Light
yellow crystals of 10 can be stored in a freezer in the
drybox for at least 1 month without decomposition, but
it is unstable at ambient temperatures (vide infra). The
1H NMR spectrum of 10 at 253 K in toluene-d8 shows
two triplets and two quartets for the hexyne ligands,
confirming the C3v structure. At higher temperatures,
the hexyne signals coalesce into a single triplet and
quartet, giving ∆Gq ) 13.8 kcal/mol at Tc ) 295 K
rot
The characterization of compound 11 is supported by
its reaction chemistry (Scheme 1). Addition of HCl to
11 recovers the tris(hexyne) fragment as the known
chloride derivative, ReCl(EtCtCEt)3.10 Passing 11
through a silica gel column converts the bis(hexyne)
fragment to the oxo-hydride 4. Reaction of 11 with
CCl4 gives CHCl3 and the chloride complex (EtCtCEt)3-
Re-NtRe(Cl)(EtCtCEt)2 (12), a classic indication of
the presence of a hydride ligand. Complex 12 is
characterized by its 1H NMR spectrum, by an [M -
hexyne]+ isotope cluster in its mass spectrum (m/z 749),
based on ∆ν ) 160 Hz. This barrier to rotation is
essentially the same as that for 3.
Deprotonation of 6 with LiNiPr2 (lithium diisopropyl-
amide, LDA) gives solutions with ambient-temperature
NMR spectra essentially identical to that of 10. Ana-
lytical data for the isolated solid indicate the presence
of 1 equiv of LiOTf, and the IR spectra of this material
show the presence of ionic triflate. Apparently, the basic
amide ligand coordinates the lithium ion and there is
hydrogen bonding between the amide and the triflate,
as the NH2 stretching mode in 10 at 3342 cm-1 splits
into bands at 3321 and 3178 cm-1 in 10‚LiOTf.
and by an IR absorption at 1085 cm-1 (νRetN-Re
;
compared to 1079 cm-1 in 11). Conversion of 11 to 12
can also be accomplished with N-chlorosuccinimide.
Complex 12 is unreactive toward water, but slowly
decomposes in air. Complexes 11 and 12 have not been
isolated in analytically pure form because of their high
solubility and thermal instability.
Complex 10 decays in solution, over 5 days at room
temperature or overnight at 50 °C, to a new rhenium
product and 0.5 equiv each of 3-hexyne and NH3.
Ammonia is not directly observed in the 1H NMR
spectrum of the reaction but can be detected by con-
densing the vapor from the reaction mixture into a
solution of 2, forming the ammonia complex 6. The
rhenium product is identified from spectroscopic data
to be the µ-nitrido complex (EtCtCEt)3Re-NtRe(H)-
(EtCtCEt)2 (11) (eq 11). Compound 11 contains a
Rh en iu m Tr is(3-h exyn e) Su lfh yd r yl Com p lex 13.
The rhenium(I) sulfhydryl complex Re(SH)(EtCtCEt)3
(13) is formed upon addition of sodium hydrosulfide,
NaSH, to the triflate complex 2 in THF (eq 12).
Recrystallization from pentane gives analytically pure
gray solids in 40% yield. Complex 13 is also generated
on reaction of H2S with the hydroxide and amido
complexes 3 and 10 (eqs 13 and 14). However, these
routes are not synthetically useful since 13 decomposes
in the presence of H2S. Compound 13 is unreactive
toward water and ammonia.
1
The H NMR spectrum of 13 shows the same pattern
as the other tris(acetylene) complexes, plus a singlet
rhenium(III) nitrido-hydride bis(3-hexyne) fragment,
closely related to the oxo-hydride 4, which serves as a
singly bonded ligand to a rhenium(I)-tris(3-hexyne)
fragment, very similar to the amine and amide com-
plexes 6-10. The tris(acetylene) unit is identified in
(23) (a) Dehnicke, K.; Stra¨hle, J . Angew. Chem., Int. Ed. Engl. 1992,
31, 955-978. (b) Nugent, W. A.; Mayer, J . M. Metal-Ligand Multiple
Bonds; Wiley-Interscience: New York, 1988 (IR studies of M(µ-N)M,
pp 121-122; structural studies, pp 179-186).

Rhenium(I) Tris(alkyne) Complexes
Organometallics, Vol. 16, No. 24, 1997 5347
Sch em e 1. Rea ction s of th e µ-Nitr id o-Hyd r id e Dim er 11
pyrolysis in the presence of CCl4 does not yield CHCl3.
Photolysis of 13 yields only ca. 0.2 equiv of free 3-hex-
yne, and photolyses in the presence of CD2Cl2 or CDCl3
do not show products that would suggest a rhenium-
hydride intermediate.
Kin etic a n d Mech a n istic Stu d ies. The kinetics of
the rearrangement of the hydroxide complex 3 to the
oxo-hydride complex 4 and free 3-hexyne (eq 2) have
been followed by 1H NMR in C6D6 solution. Plots of ln-
[3] vs time are linear to about three half-lives (Figure
3). The derived first-order rate constant, k3 ) (5.6 (
1.2) × 10-6 s-1 at 294 ( 1 K, is independent of the initial
concentration of 3 over a factor of eight. This rate
constant is also independent of the initial purity of 3,
comparing crystalline samples with crude materials. An
Eyring plot of five rate constants determined at tem-
peratures between 294 and 327 K yields the activation
parameters ∆Hq ) 17 ( 1 kcal/mol and ∆Sq ) -25 ( 5
eu. The deuteroxide complex Re(OD)(EtCtCEt)3 (3-d)
rearranges to 4-d more slowly, with kOH/kOD ) 5 ( 1 at
294 ( 1 K (Figure 3). In C6D6 saturated with water,
rearrangement of 3 is about 35% slower than in dry
solvent.
(1H) at 1.15 ppm due to the sulfhydryl proton. The
alkyne resonances broaden and coalesce at or above
The rate constant for the rearrangement of 3 is
unchanged within experimental error by the presence
of added free 3-hexyne, up to 1 M concentration.
Likewise, the presence of 1 M 2-butyne at 294 ( 1 K
does not affect the rate constant, although in addition
to 4, two minor 2-butyne-containing products are seen,
with the total concentration of bound 2-butyne about
10% of the total rhenium concentration. A small
amount of the known17 Re(O)H(MeCtCMe)2 is found
and somewhat more of a mixed butyne/hexyne material,
most likely Re(O)H(MeCtCMe)(EtCtCEt) but the data
do not rule out a rhenium(I) hydroxide Re(OH)(Me-
CtCMe)x(EtCtCEt)3-x (x ) 1 or 2). Compound 4 does
not exchange with 2-butyne under these conditions,
even when heated to 80 °C for 1 week. Therefore, the
formation of butyne-containing products must result
from ligand exchange in 3 prior to or during rearrange-
ment. The related methoxide derivative Re(OMe)-
(EtCtCEt)3 undergoes 2-butyne exchange more rapidly
room temperature, with ∆Gq ) 16.0 ( 1 kcal/mol at
rot
314 K based on the coalescence of the methyl resonances
(∆ν ) 20 Hz). The IR spectrum of 13 is very similar to
that of the hydroxide complex, with a band at 2555 cm-1
assigned as the S-H stretch. This is within the
reported range of such frequencies in metal sulfhydryl
complexes.24
Complex 13 is much more thermally robust than the
hydroxide and amido complexes 3 and 10. Benzene
solutions of 13 are indefinitely stable at ambient tem-
peratures and decompose only on heating to 150 °C for
1 week, forming NMR-silent black solids. Heating 13
and 2-butyne in C6D6 at 70 °C for 7 days does not result
1
in observable alkyne exchange by H NMR. There is
no evidence for rearrangement to a sulfido-hydride
complex, as free 3-hexyne is not detected by NMR and
(24) Mueting, A. M.; Boyle, P. D.; Wagner, R.; Pignolet, L. H. Inorg.
Chem. 1988, 27, 271.

5348 Organometallics, Vol. 16, No. 24, 1997
Tahmassebi et al.
F igu r e 4. Normalized plot of [Re(NH2)(EtCtCEt)3]t/[Re-
(NH2)(EtCtCEt)3]o versus time for two different [Re(NH2)-
(EtCtCEt)3]o.
F igu r e 3. Kinetic data for the rearrangement of Re(OX)-
(EtCtCEt)3 (X ) H, D; T ) 21 ( 1 °C).
than 3, with a half-life of only a few hours at ambient
temperatures.10
3-hexyne, which is a product of the rearrangement, it
is not surprising that the loss of starting material
follows neither simple first-order nor simple second-
order kinetics. Surprisingly the time course of the
reactionsthe fraction of 10 reacted vs timesis the same
within experimental error for the two reactions whose
concentrations of 10 differ by a factor of five (Figure 4).
The addition of small amounts (∼0.08 equiv) of
[(EtCtCEt)2ReO]Na (5) to a solution of 3 at ambient
temperature does not change the rate of rearrangement.
Complex 3 decomposes slowly in the presence of larger
amounts (∼0.8 equiv) of 5; yet the initial rate of growth
of the products in that sample remains roughly the same
as that of clean hydroxide samples. To test for the
presence of 5 as an intermediate, the rearrangement
reaction was run in the presence of p-iodotoluene, which
reacts rapidly with 5 to form a mixture of Re(O)(p-Tol)-
(EtCtCEt)2 and Re2(O)2(EtCtCEt)4.11 Neither of these
products were observed, and the rate of rearrangement
is unchanged in the presence of p-iodotoluene. In a
control experiment, 5 was added to a 1:1 mixture of
p-iodotoluene and phenol, yielding mostly 4 but also
small amounts of the trapped products. Since phenol
is a more rapid proton donor than 3 (phenol + 5 is fast,
while 3 + 5 gives 4 slowly if at all), the lack of any
trapped products in the rearrangement of 3 indicates
that 5 is not an intermediate. In addition, added 5 is
not a catalyst for the rearrangement, although catalysis
is observed in acetonitrile solutions with KOMe, KO-
tBu, and KOPh, as noted above (eq 8).
The conversion of the amido complex 10 to the
µ-nitrido dimer 11 has also been monitored by 1H NMR,
monitoring the concentrations of all of the reactants and
products via their methylene resonances. The reaction
was followed over roughly one half-life (12 h at 60 °C),
but after this time the thermal decomposition of 11
becomes significant and the data become unreliable.
Using data from a solution that was initially 0.1 M 10
in C6D6, neither the plot of ln[10] vs time nor the plot
of [10]-1 vs time are linear over this time period. The
presence of 0.5 M 2-butyne or 0.44 M 3-hexyne dramati-
cally slows the reaction. In 40 h at 60 °C, over which
time the reaction of an alkyne-free sample has gone to
completion, the samples with added alkyne show less
than 5% conversion. Added 2-butyne exchanges with
bound 3-hexyne to form a mixture of complexes Re-
(NH2)(EtCtCEt)x(MeCtCMe)3-x, x ) 0-3, with a
roughly statistical equilibrium reached within 7 h at 60
°C. Assuming that alkyne exchange occurs via a dis-
sociative mechanism, as found for tris(alkyne) alkoxide
complexes,10 the first-order rate constant is 1.9 × 10-4
s-1 at 60 °C. Given the inhibition of 10 f 11 by
Discu ssion
The rearrangement of 3 to 4 (eq 2) is the first
hydroxide to oxo-hydride rearrangement that can be
directly monitored. This transformation also undoubt-
edly occurs in the reaction of Cp*2Ta(dCH2)H with
water to give Cp*2Ta(O)H7 and likely occurs in the
formation of [Re(O)HX{(Cy2PCH2CH2CH2)2PPh}]SbF6
(X ) H, F)25 and in various reactions of the form LnM
+ H2O f LnMdO + H2.26 Amido/imido-hydride inter-
conversion appears to be facile in Re(NAr)3H (Ar ) 2,6-
iPr2C6H3) on the basis of NMR studies and reactivity.27
The amido complex 10 undergoes a similar rearrange-
ment, with hydrogen migration from N to Re and
oxidation of a Re(I) center to Re(III). But the product,
a µ-nitrido compound, and the mechanism are different
from the oxo case. The sulfhydryl complex 13 shows
no evidence of rearrangement and decomposes only at
150 °C, while 3 and 10 rearrange at ambient temper-
atures.
Th er m od yn a m ic Con sid er a tion s. The equilibri-
um constant for the rearrangement of 3 to 4 can be
estimated from the rough pKa values for 3 and 4, as
shown in Scheme 2: Keq = 109(6 M or ∆G° = -12 ( 8
kcal/mol. While the pKa values are crude numbers
derived solely from kinetic observations, the derived
equilibrium constant is consistent with the complete
conversion of 3 to 4 in the presence of 1 M 3-hexyne,
which requires that Keq g 102 M (∆G° e -2 kcal/mol).
It is also consistent with the observation that 4 does
not exchange alkyne ligands over a week at 80 °C, which
implies that the reverse reaction (4 + 3-hexyne f 3) is
very slow, ∆Gq > 32 kcal/mol. Since ∆Gq for the forward
reaction at 80 °C is 26 kcal/mol, the rearrangement
(25) Kim, Y.; Gallucci, J .; Wojcicki, A. J . Am. Chem. Soc. 1990, 112,
8600-8602.
(26) See, for instance: Hall, K. A.; Mayer, J . M. J . Am. Chem. Soc.
1992, 114, 10402-10411.
(27) Williams, D. S.; Schrock, R. R. Organometallics 1993, 12, 1148.

Rhenium(I) Tris(alkyne) Complexes
Organometallics, Vol. 16, No. 24, 1997 5349
Sch em e 2
must be favorable by at least 6 kcal/mol at this tem-
perature. The reaction involves loss of an alkyne ligand
and conversion of an O-H bond into an Re-H bond,
both of which are quite enthalpicaly unfavorable. These
processes must be compensated for by the change from
an Re-O single bond in 3 to the triple bond in 4.28 The
rhenium-hexyne bonding does not substantially change
on going from 3 to 4, as the alkynes change from 31/3-
to 3-electron donors. Rearrangement of the amido
complex 10 is likely to be similarly driven by the
formation of Re-N π bonds, although the more complex
nature of this transformation precludes such simple
thermochemical analysis. The lack of reaction of the
sulfhydryl complex 13 to a sulfido-hydride complex
could be due to a reversal in the thermodynamics, due
to the presumably weaker Re-S π bonds. Attempts to
prepare the sulfido-hydride complex from Re(S)I-
(EtCtCEt)2 led to decomposition,29 so we cannot deter-
mine whether the reverse reaction occurs. It is also
possible that the lack or reaction of 13 is due to kinetic,
rather than thermodynamic, factors. These rearrange-
ments require loss of an alkyne ligand at some stage,
which is much less facile for 13 than for 10 or 3 based
on their rates of exchange with 2-butyne.
Mech a n istic Con sid er a tion s. The rearrangements
discussed here are migratory deinsertion or R-elimina-
tion reactions of 18-electron organometallic complexes.
The typical mechanism of such processes is initial ligand
loss to give an unsaturated intermediate in which
migration takes place.2 A classic example is the revers-
ible R-elimination following loss of a ligand from Cp2W-
(CH3)L+.30 In the rhenium compounds, such a pathway
would involve initial loss of alkyne to give Re(EHx)-
(EtCtCEt)2 (EHx ) OH (A), NH2 (B), or SH (C)),
followed by rearrangement or another reaction (eq 15).
surprisingly, the migratory deinsertion of 3 to 4 does
not occur by the mechanism of eq 15. The exchange
with 2-butyne likely proceeds through A since the
analogous methoxide complex exchanges alkynes by a
dissociative pathway.10 The data do not determine
whether A can rearrange to its isomer 4, but they
indicate that this path can be at most a small fraction
of the reaction.
Three other pathways have been considered for the
conversion of 3 to 4 (Scheme 3). In path i, hydrogen
migration occurs initially to one of the alkyne ligands
to give the oxo-3-hexenyl complex Re(O)(CEtdCHEt)-
(EtCtCEt)2, which then undergoes â-hydride elimina-
tion to form 4 and 3-hexyne.32 Efforts to independently
prepare the hexenyl complex have been unsuccessful.
33
The related vinyl complex Re(O)(CHdCH2)(EtCtCEt)2
decomposes in C6D6 over 2 h to NMR-silent materials,
suggesting that the hexenyl derivative would not cleanly
eliminate to 4 and, thus, is unlikely to be an intermedi-
ate. The analogous oxo-ethyl complex, Re(O)Et-
(EtCtCEt)2, does not undergo â-hydrogen elimination
at over 100 °C in benzene solution.17
Mechanism ii involves deprotonation of 3 to 5 by an
external base. This pathway is indicated for the rapid
conversion of 3 to 4 in CD3CN when small amounts of
KOMe, KOtBu, and KOPh are added. No catalysis is
observed with the weaker base KOC6H4NO2. The flash
of dark orange is consistent with the intermediacy of 5
(eq 8). In the absence of added reagents, an adventi-
tious base would be required. This is hard to rationalize
with the observation that samples of 3 with varying
purity, from impure to crystalline, rearrange at the
same rate and that conversion to 4 proceeds at roughly
the same rate in the solid state. This also rules out
catalysis by adventitious water or another impurity (and
small amounts of H2O and MeOH inhibit the reaction).
The intermediacy of 5 in the uncatalyzed rearrangement
is also ruled out by the experiments with added p-
iodotoluene (vide supra). Surprisingly, small amounts
of the sodium salt of 5 (0.08 equiv) do not catalyze the
rearrangement. This is because protonation of 5 by 3
is slow, despite being significantly downhill (Scheme 2).
Proton transfer to metal centers is typically slower than
H+ transfers to oxygen or nitrogen,34 and there is
evidence that proton transfer reactions of metal hydrox-
ides are slow.35 Proton transfer from 3 to 5 would
appear to be sterically encumbered, and deprotonation
of 3 is accompanied by loss of an alkyne which should
contribute to a kinetic barrier.34,36 Catalysis by KOMe,
KOtBu, or KOPh is more efficient than by 5 because
The data for rearrangement of the amido complex 10
are consistent with a pre-equilibrium alkyne loss, as
there is inhibition by added 3-hexyne and 2-butyne
exchange is faster than conversion to 11.
In contrast, rearrangement of the hydroxide complex
3 is not inhibited by the presence of 1 M 3-hexyne, and
exchange with added 2-butyne is an order of magnitude
slower than conversion to 4. This rules out equilibrium
loss of 3-hexyne prior to the rate-limiting step. Alkyne
loss, k1 in eq 15, cannot be rate limiting because there
is a primary isotope effect, kOH/kOD ) 5 ( 1.31 So,
(32) We thank K. G. Caulton for this suggestion, see: Caulton, K.
G. Chemtracts: Inorg. Chem. 1993, 5, 133.
(28) Given the negative ∆G°, conversion of 3 f 4 must have a
favorable or near-zero ∆H°.
(33) Re(O)(CHdCH2)(EtCtCEt)2 was formed from Re(O)I(EtCtCEt)2
and CH2dCHMgBr/ZnCl2 as indicated by its 1H NMR spectrum.
(34) Kramarz, K. W.; Norton, J . R. Prog. Inorg. Chem. 1994, 42,
1-65.
(35) (a) Carroll, J . M.; Norton, J . R. J . Am. Chem. Soc. 1992, 114,
8744-5. (b) Erikson, T. K. G.; Mayer, J . M. Angew. Chem., Int. Ed.
Engl. 1988, 27, 1527.
(29) Tahmassebi, S. K.; Mayer, J . M. Organometallics 1995, 14,
1039.
(30) Cooper, N. J .; Green, M. L. H. J . Chem. Soc., Dalton Trans.
1979, 1121.
(31) See Supporting Information for the kinetic expressions.

5350 Organometallics, Vol. 16, No. 24, 1997
Tahmassebi et al.
Sch em e 3. P ossible P a th w a ys for Hyd r oxid e to Oxo-Hyd r id e Rea r r a n gem en t
the alkoxides and resultant alcohols circumvent the
kinetic barrier to the reaction of 3 and 5.
unimolecular rearrangement of B or bimolecular reac-
tion of two molecules of B do not have this property.31
Applying the steady-state approximation to the concen-
tration of B in this mechanism gives eq 16. Taking Co
The data, thus, indicate that rearrangement occurs
by rate-limiting hydrogen migration synchronously with
or prior to loss of ligand. Ligand loss could occur with
same-side37 or back-side displacement; the former is
arbitrarily drawn as mechanism iii in Scheme 3. An
alternative pathway of pre-equilibrium hydrogen migra-
tion followed by rate-limiting ligand loss is ruled out
by the kOH/kOD of 5 ( 1. The isotope effect calculated
for such a pre-equilibrium, based on νOH in 3 and using
νReH in 4 as a model for the intermediate, is only 2.4.
Since 3 is an 18-electron species, hydrogen migration
preceding alkyne loss would require a reduction in
π-donation from the 31/3-electron donor alkyne ligands.
The small ∆Hq of 17 kcal/mol is consistent with Re-H
σ bond and Re-O π-bond formation accompanying O-H
bond cleavage. The negative ∆Sq (-25 eu) indicates a
transition state that is more ordered than the ground
state, suggesting that alkyne dissociation is not well-
developed at the transition state.
Rearrangement of the rhenium(I) amido complex 10
to the µ-nitrido dimer 11 is also a formal 1,2-migration,
with a hydrogen atom moving from nitrogen onto
rhenium. In contrast to the hydroxide case, inhibition
by added 3-hexyne indicates that the coordinatively
unsaturated intermediate [Re(NH2)(EtCtCEt)2] (B) is
on the pathway to rearrangement (eq 15). Even though
the inhibitor hexyne is formed in the reaction, the
fraction of 10 consumed as a function of time is
independent of its starting concentration (Figure 4).
This is normally a characteristic of first-order kinetics
but it is also consistent with the first steps of the
mechanism in Scheme 4, bimolecular reaction of B with
another molecule of 10. Alternative pathways involving
d[Re(NH2)(EtCtCEt)3]
)
dt
-2k1k2[Re(NH2)(EtCtCEt)3]2
(16)
k-1[EtCtCEt] + k2[Re(NH2)(EtCtCEt)3]
as the initial concentration of 10 and X as the fraction
of starting material remaining, then [Re(NH2)(EtCtC-
1
Et)3]t ) CoX at time t and [EtCtCEt]t ) /2(Co - CoX)
when there is no added 3-hexyne. Substituting this into
eq 16 leads to eq 17 from which all the Co terms cancel
(eq 18), indicating that the time course of the reaction
is independent of Co, as observed. The time course
2
dCoX
dt
-2k1k2Co X2
)
(17)
(18)
1/2k-1(Co - CoX) + k2CoX
-2k1k2X2
1/2k-1(1 - X) + k2X
dX
dt
)
of the reaction is reasonably well fit by eq 18, given the
scatter in the data, with k1 ) 1.9 × 10-4 s-1 at 60 °C
(from the 2-butyne exchange reaction) and k-1/k2 ≈ 40.
Scheme 4 sketches a possible mechanism from 10 to
11. Nucleophilic attack of the amide lone pair of 10 on
the empty coordination site of B to form a µ-amido
species, as is typical of low-valent metal amido com-
plexes.38 The amide lone pair is basic and apparently
coordinates Li+ in 10‚LiOTf. Proton transfer from the
bridging amide to the terminal one forms a µ-imido
dimer with an ammonia coligand. Hydrogen migration
(36) Protonation of 5 at rhenium would appear to occur with only
minor rearrangement, based on the structures of [Re(O)(MeCtCMe)2]-
12
[Na(crypt)]18 and Re(O)I(MeCtCMe)2.
(37) As observed in pyridine exchange reactions in [Re(O)py-
(RCtCR)2]+, see: Mayer, J . M.; Tulip, T. H.; Calabrese, J . C.; Valencia,
E. J . Am. Chem. Soc. 1987, 109, 157-163.
(38) (a) Lappert, M. F.; Power, P. P.; Sanger, A. R.; Srivastava, R.
C. Metal and Metalloid Amides; Wiley-Interscience: New York, 1980.
(b) Fryzuk, M. D.; Mongomery, C. D. Coord. Chem. Rev. 1989, 95, 1-40.

Rhenium(I) Tris(alkyne) Complexes
Organometallics, Vol. 16, No. 24, 1997 5351
Sch em e 4. P ossible Mech a n ism for th e Rea r r a n gem en t of 10 to 11
in this complex along with loss of ammonia, similar to
the rearrangement of 3, affords the product. The data
are, thus, consistent with a 1,2-hydrogen migration step
in the rearrangement of 10 but do not require it. The
resistance of the adduct 10‚LiOTf to rearrange may be
due to the Lewis acid occupying the nitrogen lone pair
and, therefore, preventing the attack on B. Alterna-
tively, the presence of the Lewis acid may inhibit alkyne
dissociation to give B. The migration in 3 is similarly
inhibited by the formation of hydrogen bonds to water
or methanol, a form of Lewis acid complexation of the
lone pair.
may be due to an inversion of the thermochemistry such
that the sulfido-hydride complex is uphill.
Exp er im en ta l Section
Syntheses were performed using standard vacuum line and
glovebox techniques except where noted. Solvents were dried
and deoxygenated according to standard methods.39 KOH
(Mallinkrodt), NaN(SiMe3)2 (Aldrich), KOtBu (Aldrich), NH3
(Aldrich), MeNH2 (Matheson), NaNH2 (Aldrich), and NaSH
(Aldrich) were used as received. PhNH2 (Mallinkrodt) was
freshly distilled prior to use. p-Toluidine and p-nitroaniline
(Aldrich) were sublimed prior to use. KOPh, K[p-OC6H4NO2],
and KOMe were made in situ by addition of their respective
alcohols to potassium metal in toluene. Re(OTf)(EtCtCEt)3
(2)10 and (EtCtCEt)2Re(O)Na (5)18 were synthesized as de-
scribed elsewhere. Some reactions were performed in sealed
NMR tubes, and the progress of the reactions was followed by
the change in the NMR spectra. Reagents and solvent were
added to NMR tubes sealed to a ground glass joint and fitted
with a needle valve. The tubes were cooled to 77 K, degassed,
sealed with a torch, and thawed under a stream of acetone.
NMR spectra were taken on a Bruker AF300, AC200, or
WM500 spectrometer; the Bruker AF300 was used in the
variable-temperature studies, in C7D8. 1H and 13C chemical
shifts are reported in ppm downfield of SiMe4 and are
referenced to the solvent peaks: δ (multiplicity, coupling
constant, number of protons, assignment). 19F chemical shifts
are reported in ppm with CF3COOH used as an external
reference. IR spectra were taken on a Perkin-Elmer Series
Con clu sion s
The rhenium hydroxide and amide complexes Re-
(OH)(EtCtCEt)3 (3) and Re(NH2)(EtCtCEt)3 (10) rear-
range at ambient temperatures with migration of a
hydrogen from oxygen or nitrogen to the rhenium
center, a migratory deinsertion or R-elimination reac-
tion. Complex 3 forms the oxo-hydride complex Re-
(O)H(EtCtCEt)2 (4), while 10 produces the µ-nitrido
dimer (EtCtCEt)3Re-NtRe(H)(EtCtCEt)2 (11). Nei-
ther rearrangement occurs by the typical organometallic
mechanism of initial ligand loss followed by deinsertion.
The hydroxide complex 3 does appear to lose an alkyne
on the time scale of the rearrangement, but this is not
on the pathway to the oxo-hydride product. Hydrogen
migration is proposed to occur in the coordinatively
saturated tris(alkyne) species 3, either synchronously
with or prior to the loss of alkyne. A deprotonation-
reprotonation mechanism is not occurring except in the
presence of KOMe, KOtBu, or KOPh, which catalyze the
conversion of 3 to 4 via the oxo anion (EtCtCEt)2ReO-
(5). Isolated samples of 5 do not act as catalysts,
apparently because of slow proton transfer kinetics.
Rearrangement of 10 is suggested to occur by initial
alkyne loss to give Re(NH2)(EtCtCEt)2, which under-
goes rate-limiting attack by an amide ligand of another
molecule of 10. The related sulfhydryl complex Re(SH)-
(EtCtCEt)3 (13) does not rearrange up to its decompo-
sition temperature of 150 °C. The ∆G° for conversion
of 3 to 4 is -12 ( 8 kcal/mol, as derived from estimated
pKa values. The inertness of the sulfhydryl complex
1600 FT-IR spectrometer and are reported in cm-1
. Mass
spectra were taken on a Kratos Analytical spectrometer using
the direct inlet probe method. FAB-MS spectra were taken
on a VG 70 SEQ tandem hybrid instrument of EBqQ geometry.
Analytical data were determined by Canadian Microanalytical
Service, Inc.
R e(I)(E t CtCE t )3 (1). Synthesized as described else-
where15 or by the following procedure. To a solution of 4.7 g
(9.5 mmol) of Re(O)I(EtCtCEt)2 in 50 mL of benzene, 2.0 mL
(10.8 mmol, 1.1 equiv) of PMePh2, and 1.5 mL (13.2 mmol, 1.4
equiv) of 3-hexyne were syringed in. The reaction was stirred
under inert atmosphere at room temperature for 10 days. The
solvent was removed, and the remaining mixture was eluted
(39) (a) Perin, D. D.; Armarego, W. L. F. Purification of Laboratory
Chemicals, 3rd ed.; Pergamon: New York, 1988. (b) Fieser, L. F.;
Fieser, M. Reagents for Organic Synthesis; Wiley-Interscience: New
York, 1967.

5352 Organometallics, Vol. 16, No. 24, 1997
Tahmassebi et al.
down a silica gel column in the air using 5% EtOAc/hexanes.
After removal of the solvent, PMePh2 was sublimed away,
leaving 2.7 g (50% yield) of 1.
13C{1H} NMR (C6D6): 13.4, 14.6 (CH3CH2CtCCH2C′H3), 20.8,
28.2 (MeCH2CtCC′H2Me), 22.1 (NH2C6H4-p-CH3), 115.3, 129.9,
136.0, 140.5 (Re-NH2C6H4Me), 164.5, 181.4 (EtCtC′Et). 19F
NMR (C6D6): -2.27. FAB-MS: 540/538 ([M]+, 100). IR (Nujol,
NaCl): 3190, 3095 (ν(NH2)), 1614, 1572 (NH2 bend), 1288
Re(OH)(EtCtCEt)3 (3). To 0.75 g (1.3 mmol) of Re(OTf)-
(EtCtCEt)3 (2) in 35 mL of benzene was syringed 0.5 mL (28
mmol, 21 equiv) of water, and the suspension was stirred for
1 h under nitrogen. The solution was then transferred via a
cannula over 0.78 g of KOH (15 mmol, 12 equiv). The mixture
was stirred for another hour, with the solution turning from
gray-brown to yellow with formation of green-gray solids. The
solvent was removed in vacuo, and 30 mL of pentane was
transferred in. Filtration, removal of the volatiles, and re-
crystallization from pentane gave 0.21 g (38% yield) of 3 as a
faintly yellow solid. 1H NMR (C6D6, 300 K): 1.10 (t, 7 Hz, 18
H, CH3CH2CtCCH2CH′3), 2.53 (br, 1 H, Re-OH), 3.1 (br, 12
H, MeCH2CtCCH′2Me). 1H NMR (C7D8, 207 K): 1.14, 1.17
(t, 7 Hz, each 9 H, CH3CH2CtCCH2CH′3), 2.49 (br, 1 H, Re-
OH), 2.92, 3.25 (q, 7 Hz, each 6 H, MeCH2CtCCH′2Me). 13C-
{1H} NMR (C7D8, 240 K): 14.2, 14.7 (CH3CH2CtCCH2C′H3),
19.8, 29.5 (MeCH2CtCC′H2Me), 167.6, 179.0 (EtCtC′Et).
MS: 368/366 ([M - acetylene]+, 100). IR (Nujol, NaCl): 3630
(s, ν(OH)), 1748 (ν(CtC)), 1731 (w, ν(CtC)), 1304, 1253, 1152,
1064, 944, 822, 722. Anal. Calcd for C18H31ORe: C, 48.08;
H, 6.95. Found: C, 47.57; H, 6.81.
(ν(OTf)), 1222, 1030, 950, 819, 722, 639. Anal. Calcd for C26
39F3NO3ReS: C, 45.33; H, 5.71; N, 2.03. Found: C, 44.44;
H, 5.50; N, 1.93.
-
H
Re(NH2)(EtCtCEt)3 (10). A solution of 0.071 g (0.12
mmol) of 6 and 0.010 g (0.26 mmol, 2.1 equiv) of NaNH2 in 20
mL of THF was stirred for 60 min. The solvent was removed
in vacuo, and 20 mL of benzene was transferred in. After the
mixtue was stirred for 5 min and filtered, the solvent was
removed in vacuo and the solids were washed with pentane.
Recrystallization from pentane gave 0.035 g (65% yield) of 10
as a light yellow solid. 1H NMR (C6D6, 300 K): 1.02 (t, 7 Hz,
18 H, CH3CH2CtCCH2CH′3), 3.11 (q, 7 Hz, 12 H, MeCH2-
CtCCH′2Me), 6.47 (s, 2 H, ReNH2). 1H NMR (C7D8, 253 K):
1.12, 1.35 (t, 7 Hz, each 9 H, CH3CH2CtCCH2CH′3), 3.04, 3.57
(q, 7 Hz, each 6 H, MeCH2CtCCH′2Me), 7.06 (br, 2 H, ReNH2).
13C{1H} NMR (C7D8, 253 K): 14.0, 15.2 (CH3CH2CtCCH2C′H3),
19.8, 28.3 (MeCH2CtCC′H2Me), 162.8, 179.8 (EtCtC′Et).
MS: 449/447 ([M]+, 100). IR (Nujol, NaCl): 3342 (ν(NH2)),
1155, 1096, 944, 720. The thermal instability of 10 has
prevented obtaining suitable analytical data.
Re(OD)(EtCtCEt)3 (3-d ). All glassware was flame-dried,
washed with D2O, and flame-dried again. Following the
procedure for 3, 0.281g (0.623 mmol) of 2, 50 mL of benzene,
and 0.11 mL of D2O were stirred over NaOD, which was
synthesized in situ from 0.3 g of Na and excess D2O. Recrys-
tallization yielded 94 mg (43%) of pale yellow solids, which
were then washed with 1.0 mL of D2O in benzene and were
recrystallized again. The enrichment was found to be close
to 70% based on the integrals of Re-OH and the methylene
protons in the 1H NMR spectrum. IR (Nujol): 2677 (s, ν(OD));
calcd, 2633 cm-1. Other spectral data are similar to that of 3.
[Re(NH3)(EtCtCEt)3]OTf (6). A solution of 0.163 g (0.281
mmol) of 2 in 15 mL of benzene was stirred under 1 atm of
NH3 gas for 30 min. The gas and the solvent were then
removed in vacuo, and the solids were washed with pentane.
Filtration and removal of the volatiles gave 0.144 g (86% yield)
of 6 as an off-white solid. 1H NMR (C6D6): 0.94, 1.08 (t, 7 Hz,
each 9 H, CH3CH2CtCCH′2CH′3), 2.92, 3.29 (q, 7 Hz, each 6
H, MeCH2CtCCH′2Me), 6.55 (s, 3 H, ReNH3). 13C{1H} NMR
(C6D6): 13.5, 14.6 (CH3CH2CtCCH2C′H3), 20.8, 28.2 (MeC-
H2CtCC′H2Me), 163.2, 180.2 (EtCtC′Et). 19F NMR (C6D6):
-2.34. FAB-MS: 450/448 ([M]+, 100). IR (Nujol, NaCl): 3319,
3272, 3178 (ν(NH3)), 1748, 1735 (w, ν(CtC)), 1643 (NH3 bend),
(EtCtCEt)3Re-NtRe(H)(EtCtCEt)2 (11). A benzene
solution of 10 was stirred at 50 °C for 12 h, followed by the
removal of the solvent in vacuo. Attempts to purify 11 by
recrystallization, sublimation, or chromatography were unsuc-
cessful. 1H NMR (C6D6): 1.02, 1.05 (t, 7 Hz, each 6 H, Re(CH3-
CH2CtCCH2CH′3)2), 1.61, 1.62 (t, 7 Hz, each 9 H, Re(CH3-
CH2CtCCH2CH′3)3), 2.91, 3.32 (q, 7 Hz, each 6 H, Re(Me-
CH2CtCCH′2Me)3), 3.43, 3.60 (m, each 4 H, Re(MeCHH′-
CtCCH′′H′′′Me)2), 5.3 (s, 1 H, ReH). DIP-MS: 797 ([M]+), 715
([M - acetylene]+, 100). IR (Nujol, NaCl): 1930 (ν(Re-H)),
1742 (ν(CtC)), 1642, 1584, 1449, 1367, 1302, 1255, 1079
(ν(RetN-Re)), 797, 714.
(EtCtCEt)3Re-NtRe(Cl)(EtCtCEt)2 (12). A few drops
of CCl4 were added to a C6D6 solution of 11. Overnight, 1H
NMR resonances for 11 disappear and new resonances grow
in. Solvent removal in vacuo gives 12. Attempts to purify 12
from larger scale reactions were unsuccessful. 1H NMR
(C6D6): 1.08, 1.10 (t, 7 Hz, each 6 H, Re(CH3CH2CtC-
CH2CH′3)2), 1.47, 1.51 (t, 7 Hz, each 9 H, Re(CH3CH2CtC-
CH2CH′3)3), 2.87, 3.32 (q, 7 Hz, each 6 H, Re(MeCH2CtCCH′2-
Me)3), 3.6, 3.8 (m, each 4 H, Re-(MeCHH′CtCCH′′H′′′Me)2).
DIP-MS: 749 ([M - acetylene]+, 100). IR (Nujol, NaCl): 1155,
1085 (ν(RetN-Re)), 973, 938, 890, 726.
1267 (ν(OTf)), 1155, 1026, 720, 632. Anal. Calcd for C19H33
-
F3NO3ReS: C, 38.11; H, 5.56; N, 2.34. Found: C, 37.94; H,
5.36; N, 2.32.
Re(SH)(EtCtCEt)3 (13). To a mixture of 0.21 g (0.36
mmol) of 2 and 0.023 g (0.41 mmol, 1.1 equiv) of NaSH, about
15 mL of dry THF was added. The mixture was stirred for
1.5 h. The solvent was removed in vacuo, and about 20 mL of
benzene was transferred in. The solution was stirred for 5
min and filtered. Benzene was removed in vacuo. The
resulting solid was recrystallized from pentane to afford 40%
yield (0.067 g) of gray 13. 1H NMR (C6D6): 1.01, 1.08 (t, 7
Hz, each 9 H, CH3CH2CtCCH2CH′3), 1.15 (s, 1 H, ReSH), 3.12,
3.24 (q, 7 Hz, each 6 H, MeCH2CtCCH′2Me). 13C{1H} NMR
(C6D6): 13.8, 14.2 (CH3CH2CtCCH2C′H3), 22.2, 28.2 (MeCH2-
CtCC′H2Me), 164.5, 174.7 (EtCtC′Et). MS: 466/464 ([M]+,
100). IR (Nujol, NaCl): 2555 (w, ν(SH)), 1304, 1255, 1150,
1063, 944, 822, 722. Anal. Calcd for C18H31SRe: C, 46.42; H,
6.71. Found: C, 46.55; H, 6.67.
[Re(NH2CH3)(EtCtCEt)3]OTf (7). In a procedure similar
to that of 6, 0.122 g (0.210 mmol) of 2 in 15 mL of benzene
was stirred under 1 atm of CH3NH2 gas for 30 min. 1H NMR
(C6D6): 0.95, 1.07 (t, 7 Hz, each 9 H, CH3CH2CtCCH′2CH′3),
2.98, 3.27 (q, 7 Hz, each 6 H, MeCH2CtCCH′2Me), 3.77 (t, 6
Hz, 3H, NH2CH3), 7.68 (q, 6 Hz, 2 H, NH2CH3). 13C{1H} NMR
(C6D6): 13.4, 14.6 (CH3CH2CtCCH2C′H3), 21.6, 27.9 (MeC-
H2CtCC′H2Me), 36.5 (NH2CH3), 164.2, 182.1 (EtCtC′Et). 19
F
NMR (C6D6): -2.27. FAB-MS: 464/462 ([M]+, 100). IR (Nujol,
NaCl): 3260, 3166 (ν(NH2)), 1749 (w, ν(CtC)), 1607 (NH2
bend), 1278 (ν(OTf)), 1243, 1155, 1032, 944, 720, 632. Anal.
Calcd for
C20H35F3NO3ReS: C, 39.20; H, 5.56; N, 2.29.
Found: C, 38.89; H, 5.71; N, 2.28.
[Re(NH2C6H4-p-CH3)(EtCtCEt)3]OTf (8). A solution of
0.197 g (0.331 mmol) of 2 and 0.037 g (0.35 mmol, 1.02 equiv)
of p-CH3C6H4NH2 in 15 mL of benzene was stirred for 2 h.
After the solvent was removed in vacuo, the solids were
washed with pentane. Filtration and removal of the volatiles
gave 8 as an off-white solid. 1H NMR (C6D6): 0.98, 1.04 (t, 7
Hz, each 9 H, CH3CH2CtCCH′2CH′3), 2.13 (s, 3 H, NH2C6H4-
p-CH3), 3.03, 3.17 (q, 7 Hz, each 6 H, MeCH2CtCCH′2Me),
7.06, 7.82 (d, each 2 H, NH2C6H4Me), 9.59 (s, 2 H, NH2Tol).
Re(O)(CHdCH2)(EtCtCEt)2 (14). Vinylmagnesium bro-
mide in THF (0.6 mL, 1 M, 0.6 mmol) was added slowly to
0.13 g (0.98 mmol, 1.6 equiv) of ZnCl2 in 10 mL of THF at
-78 °C. White solids formed, and the yellow mixture was
slowly warmed to room temperature and stirred for 1 h. The
suspension was then slowly added via a syringe to a -78 °C
solution of 0.113 g (0.23 mmol, 0.4 equiv) of Re(O)I(EtCtCEt)2
in 25 mL of THF. It was stirred for 3 h, after which time the
solvent was removed in vacuo. Benzene (30 mL) was trans-

Rhenium(I) Tris(alkyne) Complexes
Organometallics, Vol. 16, No. 24, 1997 5353
ferred in, and the solution was stirred for 5 min and filtered.
Benzene was removed in vacuo to give 14 as an oil. Complex
14 is thermally unstable and decomposes to an NMR-silent
material within 2 h. 1H NMR (C6D6): 1.15, 1.21 (t, 7 Hz, each
6 H, CH3CH2CtCCH2CH′3), 2.9 (m, 8 H, MeCHH′CtCC-
H′′H′′′Me), 5.4 (d of d, J gem ) 1 Hz, J trans ) 18 Hz, ReCHd
CHcisHtrans), 6.1 (d of d, J gem ) 1 Hz, J cis ) 13 Hz, Re-
CHdCHcisHtrans); the peak for ReCHdCH2 was not identified.
Kin etics. C6D6 (Cambridge Isotope), 3-hexyne, and 2-bu-
tyne were dried over sodium overnight and were vacuum
transferred prior to use. Ferrocene was either weighed on an
analytical balance on the bench top and degassed at -77 °C
prior to entering the glovebox or sublimed in vacuo and
weighed in the glovebox. In the glovebox, stock solutions
(C6D6) of Cp2Fe and 3 or 10 were prepared, and appropriate
quantities of these solutions, 3-hexyne, and C6D6 were syringed
into NMR tubes to attain a volume of 400 µL. For the sample
with 2-butyne, the alkyne was vacuum transferred into the
NMR tube. The NMR tubes were cooled in liquid nitrogen,
sealed with a torch, and thawed immediately prior to use.
In the ambient-temperature kinetic studies of 3 f 4, the
tubes were kept in an insulated, room-temperature (21 ( 1
°C) water bath. For the high-temperature experiments, the
tubes were placed in the NMR probe at room temperature.
After completing the lock and shim processes, the temperature
control unit was set to the desired temperature and the
automated acquisition program was activated. The shims
were later adjusted as the sample temperature rose to the
designated temperature. The actual temperature was calcu-
lated using a methanol sample.40 Concentrations were calcu-
lated by integrating the hydride resonance of 4 (δ 6.02) and
the methylene resonances (δ 2.0) of free 3-hexyne vs a
ferrocene standard (δ 4.00). The concentration of Re(O)D-
(EtCtCEt)2 (4-d ) was found by subtracting the concentration
of 4 from the concentration of the free 3-hexyne. In the kinetic
studies of 10 f 11, the tubes were kept in an oil bath at 59.7
( 0.4 °C. At appropriate times, the tubes were removed and
NMR spectra obtained at room temperature. The concentra-
tions of 11, 12, and free alkyne were calculated by integrating
the methylene resonances vs Cp2Fe.
disorder, though not involving any of the atoms in the rhenium
coordination sphere. Disorder in the ethyl groups was modeled
with two equal occupancy sites for C(1), C(2), C(6), C(7), C(11),
C(12), C(13), C(14), C(17), and C(18). Figure 1 shows the set
of ligand carbons that best fit on the planes containing Re,
O(1), and the acetylenic carbons for each ligand. The smeared
electron density of the CF3 group was modeled with seven
fluorine atoms around the carbon (F1, F1A, F2, and F2A at
50% occupancy and F3, F3A, and F3B at 33% occupancy).
X-r a y Cr ysta llogr a p h ic Str u ctu r e Deter m in a tion of
Re(OH)(EtCtCEt)3 (3). Clear crystals were grown by the
slow evaporation of a saturated pentane solution of 3 in the
glovebox freezer. A crystal was mounted with stopcock grease
in a cold nitrogen stream (-60 °C) on an Enraf-Nonius CAD4
diffractometer. A unit cell was obtained from 25 reflections
in the range 2θ ) 26-34°, and data were collected with
minimal decay (Table 1). A spherical absorption correction
was applied, as it gave a better R of averaging (2.7%) than an
empirical correction (3.4%). The cell errors, the soft and oily
nature of the crystal, and the broad diffraction peaks suggested
less than optimal crystal quality. The data was refined in
P21/m using Siemens SHELXTL PLUS (PC Version), initially
with anisotropic thermal parameters for all non-hydrogen
atoms, to R ) 7.9%, Rw ) 7.9%, and goodness of fit ) 1.50. In
this space group, the rhenium, oxygen, and one of the hexyne
ligands lie in a mirror plane. Anisotropic thermal parameters
for three of the atoms, O(1), C(1), and C(9) (two of which lie
on the mirror plane), were nonpositive definite. This may
reflect a disorder problem, possibly involving the mirror plane,
but alternative refinements in the acentric space group P21
were no better, and statistical tests did not provide strong
guidance (presumably because the scattering is dominated by
the rhenium atom). No attempts were made to model any
disorder because of the data quality and the lack of any
indication of disorder in the difference maps. Because of the
nonpositive definite thermal parameters, final refinement in
P21/m was done with all carbon and oxygen atoms refined
isotropically. The hydroxide hydrogen was placed on a reason-
able peak in the electron-density map.
Ack n ow led gm en t. We are grateful to the U.S.
National Science Foundation for primary financial sup-
port, to the National Sciences and Engineering Research
Council of Canada for a fellowship to W.S.M., and to
the donors of the Petroleum Research Fund, adminis-
tered by the American Chemical Society, for initial
support. We thank Dr. David Barnhart (UW) for the
X-ray crystal structures.
X-r a y Cr ysta llogr a p h ic Str u ctu r e Deter m in a tion of
Re(OTf)(EtCtCEt)3 (2). Clear crystals were grown by the
slow evaporation of a saturated pentane solution in the
glovebox. A fragment was encased in epoxy on a glass fiber
and transferred to an Enraf-Nonius CAD4 diffractometer. A
unit cell was obtained from 25 reflections in the range 2θ )
24-30° (Table 1). A high-ø (88°) reflection was scanned to
provide for an absorption correction. The intensity of standard
reflections decayed substantially (75%) during data collection,
without loss of orientation. Reduction of data was carried out
using XCAD4, and all further work was carried out using the
PC version of Siemens SHELX. The Laue merging R factor
was 1.6% for 345 reflections, indicating that the decay factors
were applied well. The structure was solved from direct
methods, and full refinement showed a large amount of
Su p p or tin g In for m a tion Ava ila ble: Text giving the
derivations of the kinetic equations for alternative pathways
for the rearrangements of 3 and 10 and tables of atom
positional and thermal parameters and bond distances and
angles for 2 (8 pages). Crystallographic details for 3 are
available as Supporting Information for ref 9. Ordering
information is given on any current masthead page.
(40) Gordon, A. J .; Ford, R. A. The Chemist’s Companion; Wiley-
Interscience: New York, 1972.
OM9704814