Formation of the 1,4-diazabutadien-2-yl complex [Mn(CNPh*)4{C(=NPh*)C(CH3)=N(Ph*)}] through methylation of a manganese(-I) isonitrilate

Article abstract of DOI:10.1021/om970287h

Alkylation of [Mn(CNPh*)₅]^- with CH₃I gives the 1,4-diazabutadien-2-yl complex [Mn-(CNPh*)₄{C(=NPh*)C(CH₃)=N(Ph*)}] (2) in a 30% yield, as established by a single-crystal X-ray diffraction study. The same product can be obtained in poor yield when CH₃OSO₂-CF₃ is used as the alkylating agent, and use of ethyl iodide gives the corresponding ethyl complex [Mn(CNPh*)₄{C(=NPh*)C(CH₂CH ₃)=N(Ph*)}] (3). It is proposed that the first step in the formation of 2 is alkylation at manganese: transient [Mn(CNPh*)₅CH₃] is then converted into an iminoacyl complex by isonitrile/alkyl insertion. Insertion of a second isonitrile into the metal-iminoacyl bond leads to the 1,4-diazabutadien-2-yl complex. The addition of free CNPh* to the reaction solution leads to only a modest increase in the yield of 2, but the importance of exogenous isonitrile is supported by the formation of [Mn(CN^t-Bu)(CNPh*)₃{C(=NPh*)C(CH ₃)=N(Ph*)}] (4), in which 1 equiv of CN^tBu is coordinated to Mn, when CN^tBu is added to a solution of 1^- before reaction with CH₃I.

Full text of DOI:10.1021/om970287h

Organometallics 1997, 16, 4109-4114
4109
F or m a tion of th e 1,4-Dia za bu ta d ien -2-yl Com p lex
[Mn (CNP h *)4{C(dNP h *)C(CH3)dN(P h *)}] th r ou gh
Meth yla tion of a Ma n ga n ese(-I) Ison itr ila te
Tracy L. Utz, Patricia A. Leach, Steven J . Geib,† and N. J ohn Cooper*
Department of Chemistry and Materials Research Center, University of Pittsburgh,
Pittsburgh, Pennsylvania 15260
Received April 7, 1997X
Alkylation of [Mn(CNPh*)5]- with CH3I gives the 1,4-diazabutadien-2-yl complex [Mn-
(CNPh*)4{C(dNPh*)C(CH3)dN(Ph*)}] (2) in a 30% yield, as established by a single-crystal
X-ray diffraction study. The same product can be obtained in poor yield when CH3OSO2-
CF3 is used as the alkylating agent, and use of ethyl iodide gives the corresponding ethyl
complex [Mn(CNPh*)4{C(dNPh*)C(CH2CH3)dN(Ph*)}] (3). It is proposed that the first step
in the formation of 2 is alkylation at manganese: transient [Mn(CNPh*)5CH3] is then
converted into an iminoacyl complex by isonitrile/alkyl insertion. Insertion of a second
isonitrile into the metal-iminoacyl bond leads to the 1,4-diazabutadien-2-yl complex. The
addition of free CNPh* to the reaction solution leads to only a modest increase in the yield
of 2, but the importance of exogenous isonitrile is supported by the formation of [Mn(CNt-
Bu)(CNPh*)3{C(dNPh*)C(CH3)dN(Ph*)}] (4), in which 1 equiv of CNtBu is coordinated to
Mn, when CNtBu is added to a solution of 1- before reaction with CH3I.
In tr od u ction
More recently we have begun to examine areas in
which the parallels between isonitrilates and carbon-
ylmetalates do not hold. We now wish to report, as
summarized in Scheme 1, examples in which the
combination of the high nucleophilicity of an isonitrilate
with the high propensity of isonitriles to undergo
insertion reactions9,10 results in alkylation-induced
coupling of two isonitrile ligands to form a structurally
characterized 1,4-diazabutadien-2-yl complex of man-
ganese similar to those previously reported by Alex-
ander as the products of PdO-catalyzed double isonitrile
insertion into manganese-aryl bonds.11
Recent reports from our laboratory on the chemistry
of isonitrilates,1 guided by the obvious analogy between
isonitrilates and carbonylmetalates, have established
close structural and reactivity parallels between these
two classes of molecules. Structural parallels include
those between the tetrahedral Co(-I) complex [Co-
(CNPh*)4]- (Ph* ) 2,6-(CH3)2C6H4)2 and the isoelec-
tronic carbonylmetalate [Co(CO)4]- 3 and between the
trigonal bipyramidal Mn(-I) complex [Mn(CNPh*)5]- 4
and [Mn(CO)5]-;5 reactivity parallels include the de-
rivatization of both [Co(CNPh*)4]- and [Mn(CNPh*)5]-
by electrophilic addition of Ph3SnCl in a manner similar
to that used by our group6 and by Ellis7 to characterize
highly reactive carbonylmetalates and the use of both
Ph3SnCl addition and the formation of metallocycles
from R,ω-dihaloalkanes to establish the existence of the
Exp er im en ta l Section
Gen er a l P r oced u r es. All reactions and manipulations
were carried out under an atmosphere of nitrogen by means
of standard Schlenk techniques or a Vacuum Atmospheres
Dry-lab glovebox unless otherwise noted. Glassware was oven-
dried or flamed under vacuum. Celite 545 (Fisher) was oven
dried (24 h) prior to use. Tetrahydrofuran (THF) was first
dried over sodium wire for at least 12 h and then distilled from
molten potassium. Pentane was pretreated with 5% nitric
acid/sulfuric acid and then potassium carbonate and distilled
from calcium hydride. All solvents were freshly distilled and
deoxygenated immediately prior to use. The following re-
agents were purchased from commercial sources: methyl
iodide (Aldrich), tert-butyl isocyanide (Aldrich), ethyl iodide
(Aldrich), and 2,6-dimethylphenyl isocyanide (Fluka).
t
Ru(-II) isonitrilates [Ru(CNR)4]2- (R ) Ph* and Bu).8
† Address crystallographic correspondence to this author.
X Abstract published in Advance ACS Abstracts, August 15, 1997.
(1) Homoleptic isonitrile complexes of metals in negative oxidation
states.
(2) (a) Warnock, G. F.; Cooper, N. J . Organometallics 1989, 8, 1826.
(b) Leach, P. A.; Geib, S. J .; Corella, J . A.; Warnock, G. F.; Cooper, N.
J . J . Am. Chem. Soc. 1994, 116, 8566.
(3) (a) Klu¨fers, P. Z. Kristallogr. 1984, 167, 253. (b) Schussler, D.
P.; Robinson, W. R.; Edgell, W. F. Inorg. Chem. 1974, 13, 153.
(4) Utz, T. L.; Leach, P. A.; Geib, S. J .; Cooper, N. J . Chem. Commun.
1997, 847.
(5) (a) Frenz, B. A.; Ibers, J . A. Inorg. Chem. 1972, 11, 1109. (b)
Heberhold, M.; Wehrmann, F.; Neugebauer, D.; Huttner, G. J . Orga-
nomet. Chem. 1978, 152, 329. (c) Balbach, B.; Baral, S.; Biersack, H.;
Herrmann, W. A.; Labinger, J . A.; Scheidt, W. R.; Timmers, F. J .;
Ziegler, M. L. Organometallics 1992, 11, 35. (d) Ben Laarab, H.;
Chaudret, B.; Dahan, F.; Devillers, J .; Poilblanc, R.; Sabo-Etienne, S.
New J . Chem. 1990, 14, 321. (e) Petz, W.; Weller, F. Z. Naturforsch.
1991, B46, 297.
(8) Corella, J . A.; Thompson, R. L.; Cooper, N. J . Angew. Chem., Int.
Ed. Engl. 1992, 31, 83.
(9) (a) Treichel, P. M. Adv. Organomet. Chem. 1973, 11, 21. (b)
Yamamoto, Y. Coord. Chem. Rev. 1980, 32, 193. (c) Singleton, E.;
Oosthuizen, M. E. Adv. Organomet. Chem. 1983, 22, 209.
(10) Durfee, L. D.; Rothwell, I. P. Chem. Rev. 1988, 88, 1059.
(11) Motz, P. L.; Alexander, J . J .; Ho, D. H. Organometallics 1989,
8, 2589.
(6) Leong, V. S.; Cooper, N. J . Organometallics 1987, 6, 2000 and
references therein.
(7) Ellis, J . E. Adv. Organomet. Chem. 1990, 31, 1.
S0276-7333(97)00287-2 CCC: $14.00 © 1997 American Chemical Society

4110 Organometallics, Vol. 16, No. 19, 1997
Utz et al.
{(CH3)2C6H3}), 150.0-120.0 (m, 36 C, CN(CH3)2C6H3), 27-10
Sch em e 1
(m, 13 C, CN(CH3)2C6H3 and CH3). Anal. Calcd for C55H57
-
MnN6: C, 77.1; H, 6.8; N, 9.8. Found: C, 76.5; H, 6.9; N, 9.3.
P r ep a r a t ion of [Mn (CNP h *)4{C(dNP h *)C(CH 3)dN-
(P h *)}] fr om CH3OSO2CF 3. This reaction was carried out
in a manner similar to that described above, except that 11
µL of a 0.01 mol L-1 solution of CH3OSO2CF3 in THF (0.10
mmol, 1 equiv) was added to the solution of [K(18-C-6)][Mn-
(CNPh*)5] in place of CH3I. After recrystallization from
pentane, this gave a 0.005 g yield (0.006 mmol, 6%) of [Mn-
1
(CNPh*)4{C(dNPh*)C(CH3)dN(Ph*)}] (IR, H NMR).
P r ep a r a t ion of [Mn (CNP h *)4{C(dNP h *)C(CH 3)dN-
(P h *)}] in th e P r esen ce of F r ee CNP h *. This reaction was
carried out in a manner similar to that described above, except
that 0.023 g (0.18 mmol, 1.8 equiv) of CNPh* was added to
the solution of [K(18-C-6)][Mn(CNPh*)5] before the addition
of CH3I. After recrystallization from pentane, this gave a 0.027
g yield (0.032 mmol, 32%) of [Mn(CNPh*)4{C(dNPh*)C-
1
(CH3)dN(Ph*)}] (IR, H NMR).
P r ep a r a tion of [Mn (CNP h *)4{C(dNP h *)C(CH2CH3)dN-
(P h *)}] (3). To a blood red solution of [K(18-C-6)][Mn-
(CNPh*)5] (0.10 g, 0.10 mmol) in 10 mL of THF was added
neat CH3CH2I (9 µL, 0.11 mmol). The solution immediately
underwent a color change to cherry red and was allowed to
stir for 30 min. The solvent was removed under reduced
pressure at low temperature (<0 °C) to give a red residue, and
the product was extracted with pentane. Concentration of the
pentane solution under reduced pressure and reduction of the
temperature to -78 °C gave 0.020 g of red crystals of [Mn-
(CNPh*)4{C(dNPh*)C(CH2CH3)dN(Ph*)}] (0.023 mmol, 23%).
IR (THF, νCN): 2057 (m), 1963 (s) cm-1
.
1H NMR (dichlo-
Infrared spectra were recorded on a Perkin Elmer 783
grating spectrophotometer with polystyrene as an external
standard. Solutions were loaded via small-bore steel cannula
into 0.1-mm NaCl cells (Teflon seals) fitted with 5-mm septa.
Nujol mulls were prepared under an inert atmosphere in a
drybox and were loaded onto NaCl plates unless otherwise
noted. All NMR spectra were recorded on a Bruker AF 300
spectrometer (1H, 300.13 MHz). Deuterated solvents were
purchased from Aldrich. Microanalyses were carried out by
Atlantic Microlab, Inc., Norcross, GA. Samples of [K(18-C-6)]-
[Mn(CNPh*)5] were prepared as reported previously4 and
stored under nitrogen at -30 °C before use.
romethane-d2): δ 7.04-6.72 (m, 15 H, CN(CH3)2C6H3), 6.62
(d, 2 H, CN(CH3)2C6H3), 6.19 (t, 1 H, CN(CH3)2C6H3), 2.42 (s,
12 H, CN(CH3)2C6H3), 2.40 (s, 6 H, CN(CH3)2C6H3), 2.38 (s, 6
H, CN(CH3)2C6H3), 2.22 (q, 2 H, CH2CH3), 1.94 (or 1.89) (s, 6
H, C{dN(CH3)2C6H3}C(CH2CH3)dC{N(CH3)2C6H3}), 1.89 (or
1.94) (s, 6 H, C{dN(CH3)2C6H3}C(CH2CH3)dC{N(CH3)2C6H3}),
1.17 (t, 2 H, CH2CH3). Anal. Calcd for C56H59MnN6: C, 77.2;
H, 6.8; N, 9.7. Found: C, 77.3; H, 7.0; N, 9.6.
P r ep a r a tion of [Mn (CNtBu )(CNP h *)3{C(dNP h *)C(C-
H3)dN(P h *)}] (4). To a blood red solution of [K(18-C-6)][Mn-
(CNPh*)5] (0.20 g, 0.20 mmol) in 10 mL of THF was added
neat tert-butyl isocyanide (23 µL, 0.20 mmol). A neat aliquot
of CH3I (15 µL, 0.24 mmol) was added to the THF solution,
immediately giving a cherry red colored solution. After the
solution had stirred for 30 min, the THF was removed under
reduced pressure and the residue extracted into pentane.
Concentration of the pentane solution under reduced pressure,
P r ep a r a t ion of [Mn (CNP h *)4{C(dNP h *)C(CH 3)dN-
(P h *)}] (2) fr om CH3I. To a blood red solution of [K(18-C-
6)][Mn(CNPh*)5] (0.10 g, 0.10 mmol) in 10 mL of THF was
added neat CH3I (7 µL, 0.16 mmol). The solution immediately
underwent a color change to cherry red. After the solution
had stirred for 1 h, the solvent was removed under reduced
pressure without warming to give a red residue. The product
was extracted with pentane, and concentration of the pentane
followed by recrystallization at -78°C, yielded 0.025 g of [Mn-
(CNtBu)(CNPh*)3{C(dNPh*)C(CH3)dN(Ph*)}] (0.031 mmol,
16%) as a red solid. IR (THF, νCN): 2055 (s), 1950 (m, br) cm-1
solution followed by cooling to -78 °C yielded 0.025 g of [Mn-
(CNPh*)4{C(dNPh*)C(CH3)dN(Ph*)}] (0.029 mmol, 30%) as
.
1H NMR (dichloromethane-d2): δ 7.04-6.55 (m, 14 H, CN-
(CH3)2C6H3), 6.23 (t, 1 H, CN(CH3)2C6H3), 2.40 (m, 18 H, CN-
(CH3)2C6H3), 2.05 (or 1.96) (s, 6 H, C{dN(CH3)2C6H3}C(CH3)dC-
{N(CH3)2C6H3}), 1.96 (or 2.05) (s, 6 H, C{dN(CH3)2C6H3}C-
(CH3)dC{N(CH3)2C6H3}), 1.78 (s, 3 H, CH3), 1.51 (s, 9 H, CNC-
(CH3)3). Anal. Calcd for C51H57MnN6: C, 75.7; H, 7.1; N, 10.4.
Found: C, 75.0; H, 7.4; N, 9.4.
red crystals. IR (Nujol, νCN): 2010 (w), 1955 (s) cm-1 1H NMR
.
(dichloromethane-d2): δ 7.12-6.75 (m, 15 H, CN(CH3)2C6H3),
6.61 (d, 2 H, CN(CH3)2C6H3), 6.20 (t, 1 H, CN(CH3)2C6H3), 2.41
(s, 12 H, mutually trans CN(CH3)2C6H3), 2.37 (s, 6 H, CN-
(CH3)2C6H3), 2.34 (s, 6 H, CN(CH3)2C6H3), 1.97 (or 1.91) (s, 6
H, C{dN(CH3)2C6H3}C(CH3)dN{(CH3)2C6H3}), 1.91 (or 1.97)
(s, 6 H, C{dN(CH3)2C6H3}C(CH3)dN{(CH3)2C6H3}), 1.84 (s, 3
H, CH3). 13C NMR (dichloromethane-d2): δ 222.22 (s, 1 C, CN-
(CH3)2C6H3), 203.89 (s, 1 C, CN(CH3)2C6H3), 197.81 (s, 1 C,
CN(CH3)2C6H3), 195.71 (s, 1 C, CN(CH3)2C6H3), 187.19 (or
154.5) (s, 1 C, C{dN(CH3)2C6H3}C(CH3)dN{(CH3)2C6H3}),
154.5 (or 187.19) (s, 1 C, C{dN(CH3)2C6H3}C(CH3)dN-
X-r a y Diffr a ction Stu d y of [Mn (CNP h *)4{C(dNP h *)C-
(CH3)dN(P h *)}]. Crystals of 2 suitable for crystallographic
analysis were grown by slow diffusive mixing of pentane into
a concentrated toluene solution of the product at -30 °C over

Formation of [Mn(CNPh*)4{C(dNPh*)C(CH3)d(NPh*)}]
Organometallics, Vol. 16, No. 19, 1997 4111
Ta ble 1. Su m m a r y of Cr ysta l Da ta , Da ta
Collection , a n d Refin em en t P a r a m eter s for
Ta ble 2. Selected Bon d Len gth s (Å) a n d
An gles (d eg) w ith in
[Mn (CNP h *)4{C(dNP h *)C(CH3)dN(P h *)}]
[Mn (CNP h *)4{C(dNP h *)C(CH3)dN(P h *)}]
Crystal Data
Mn-C(3)
Mn-C(5)
Mn-C(4)
Mn-C(6)
Mn-C(2)
Mn-N(1)
Mn-C(1)
C(1)-N(1)
C(1)-C(2)
C(1)-C(7)
N(1)-C(16)
1.802(5)
1.847(5)
1.849(5)
1.861(5)
2.020(4)
2.104(4)
2.564(5)
1.272(5)
1.468(6)
1.484(6)
1.414(6)
N(2)-C(2)
N(2)-C(26)
N(3)-C(3)
N(3)-C(36)
C(4)-N(4)
N(4)-C(46)
C(5)-N(5)
N(5)-C(56)
C(6)-N(6)
N(6)-C(66)
1.264(5)
1.409(6)
1.174(5)
1.371(6)
1.179(5)
1.386(6)
1.168(6)
1.373(6)
1.155(5)
1.381(6)
formula
cryst syst
space group
a, Å
b, Å
c, Å
C55H57MnN6‚0.5C5H12
triclinic
P1h
12.586(12)
14.341(10)
16.047(12)
68.08(5)
69.53(7)
76.14(7)
2497(3)
2
R, deg
â, deg
γ, deg
V, Å3
Z
C(3)-Mn-C(2)
C(5)-Mn-C(2)
C(4)-Mn-C(2)
C(6)-Mn-C(2)
C(3)-Mn-N(1)
C(5)-Mn-N(1)
C(4)-Mn-N(1)
C(6)-Mn-N(1)
C(2)-Mn-N(1)
N(1)-C(1)-C(2)
N(1)-C(1)-C(7)
C(2)-C(1)-C(7)
C(1)-N(1)-C(16)
99.5(2)
161.0(2)
96.8(2)
86.0(2)
163.6(2)
97.1(2)
93.7(2)
91.7(2)
64.4(2)
106.5(3)
126.7(4)
126.7(4)
126.1(4)
C(16)-N(1)-Mn
C(2)-N(2)-C(26)
N(2)-C(2)-C(1)
N(2)-C(2)-Mn
C(1)-C(2)-Mn
C(3)-N(3)-C(36)
N(3)-C(3)-Mn
N(4)-C(4)-Mn
C(4)-N(4)-C(46)
N(5)-C(5)-Mn
C(5)-N(5)-C(56)
N(6)-C(6)-Mn
C(6)-N(6)-C(66)
137.7(3)
119.6(3)
118.7(4)
148.0(3)
93.3(3)
169.1(4)
175.8(4)
170.8(4)
157.9(4)
175.8(4)
175.6(5)
178.7(4)
172.9(4)
F (calcd), g cm-3
1.188
Data Collection
µ, cm-1
temp, °C
cryst dimens, mm
radiation
3.07
-65(2)
0.21 × 0.22 × 0.32
Mo KR (λ ) 0.710 73 Å),
graphite-monochromated
Siemens P3
variable, 3-20
3.82 < 2θ < 45
ω
diffractometer
scan speed, deg min-1
2θ scan range, deg
scan technique
data collected
+h, (k, (1
0.100
6537
3/197
weighting factor, g
unique data
standard reflns
data collection and refinement are contained in the Siemens
program packages P3 and SHELXTL PLUS.12
Agreement Factors
R(F), % (based on 6537 data, Fo > 4σ(Fo))
wR(F2), % (all data)
GOF (on F2)
5.95
18.02
1.053
0.440, -0.351
11.27
0.001
Resu lts a n d Discu ssion
Alkylation of [Mn(CNPh*)5]- was examined by addi-
tion of 1 equiv of CH3I to a blood red THF solution of
[K(18-C-6)][Mn(CNPh*)5] ([K(18-C-6)]1), prepared as
previously reported by naphthalenide reduction of [Mn-
(CNPh*)5Cl] at -78 °C.4 This resulted in an immediate
color change from blood red to cherry red, together with
a shift in the IR bands assigned to the isonitrile ligands
from 1920 and 1710 cm-1 to 2010 and 1955 cm-1. This
large shift is consistent with the formation of a product
in which the isonitrile ligands are coordinated to a
neutral metal center, and it was possible to isolate a
nonpolar product which could be recrystallized from
pentane. This material is not completely stable at
ambient temperatures, and cherry red THF solutions
acquire a greenish hue when left at room temperature
for more than 30 min. It was, however, immediately
clear from inspection of 1H NMR spectra that this was
not the simple methyl adduct [Mn(CNPh*)5CH3] which
would be the product of an SN2 addition of CH3I to 1-,
as expected if the reaction had paralleled the addition
of CH3I to [Mn(CO)5]- to form [Mn(CO)5CH3].13
max peak, e Å-3
data/parameter
∆/σ
a period of weeks. The crystals rapidly powdered when
removed from the mother liquor, presumably as a consequence
of loss of a volatile pentane of solvation from the crystal lattice
(see below), but a suitable crystal was eventually mounted by
coating it in Fluorolube and rapidly cooling the crystal to ca.
-65 °C in a stream of cold N2.
Axial photographs confirmed the crystal quality, and sys-
tematic absences did not reveal any crystal symmetry higher
than triclinic. The centrosymmetric space group P1h was
chosen on the basis of E-values and confirmed by the successful
solution and refinement of the structure. Unit-cell dimensions
were derived from the least-squares fit of the angular settings
of 25 reflections with 18° e 2θ e 25°. Diffraction data were
collected on a Siemens P3 diffractometer. Data collection
parameters and other crystallographic data are summarized
in Table 1. A semi-empirical absorption correction was applied
to the diffraction data using the program XEMP. No decay
was observed in three standard reflections during the data
collection.
The structure was solved using the direct methods program
TREF, which located the Mn atom. The remaining non-
hydrogen atoms were located from subsequent difference
Fourier syntheses and were refined anisotropically. The
crystal contained a pentane molecule disordered about an
inversion center. The molecule was modeled in two orienta-
Str u ctu r a l Ch a r a cter iza tion of [Mn (CNP h *)4-
{C(dNP h *)C(CH3)dN(P h *)}] (2). Growing X-ray qual-
ity crystals of the methylation product was difficult,
partly because of the limited stability of the material
in solution at room temperature, but it was eventually
determined that suitable crystals of a pentane solvate
could be grown by slow diffusive mixing of pentane into
a concentrated toluene solution of the product at -30
°C. A single-crystal diffraction study of the red blocks
obtained in this way was carried out as described in the
1
tions, each with /2 occupancy. Idealized atomic positions were
calculated for all hydrogen atoms except those anticipated for
pentane (d(C-H) ) 0.96 Å, U ) 1.2U of the attached carbon
atom). The final difference Fourier syntheses showed only a
diffuse background (maximum contour 0.45 e/Å3). Inspections
of Fo vs Fc values and trends based upon sin θ, Miller indeces,
and parity groups failed to reveal any systematic errors in the
X-ray data. Atomic coordinates for 2 are listed in the Sup-
porting Information, and selected bond lengths and angles are
given in Table 2. All of the computer programs used in the
(12) Sheldrick, G. M. SHELXTL User’s Manual, Issue 5.1; Sie-
mens: Madison, WI, 1994.
(13) (a) Clossen, R. D.; Kozikowski, J .; Coffield, T. H. J . Org. Chem.
1957, 22, 598. (b) King, R. B. Acc. Chem. Res. 1970, 3, 417.

4112 Organometallics, Vol. 16, No. 19, 1997
Utz et al.
C(1)-N(1) and C(2)-N(2) bond lengths of 1.273(5) and
1.266(5) Å, for example, are close to the C(sp2)dN(2)
average of 1.279 Å in the Car-CdN-C# group, as cited
in a statistical study,17 and the C(1)-C(2) bond length
of 1.468(6) Å is similar to the average value of 1.455 Å
for conjugated C(sp2)-C(sp2) bonds.17 The bond lengths
of the 1,4-diazabutadien-2-yl ligand in 2 are also similar
to those in those seen in earlier examples of this
functional group. Alexander, for example, has re-
ported11 CdN bond lengths of 1.287(4) and 1.274(4) Å
(for the in-ring and out-of-ring bonds, respectively) and
a C-C bond length of 1.490(5) Å in [Mn(CO)4{C(dN-p-
tolyl)C(CH2C6H4-p-OMe)dN(p-tolyl)}], in good agree-
ment with the corresponding bond lengths in 2.
The sp2 geometries of C(1), N(1), and C(2) would lead
one to expect a planar geometry for the 1,4-diazabuta-
dien-2-yl ligand, and indeed none of the constituent
atoms are more than 0.03 Å out of the least-squares
plane containing Mn, C(1), C(2), C(7), and N(1).
The Mn-C bond distances involving the terminal
isonitrile ligands average 1.840 Å; this is somewhat
shorter than the average values of 1.869 Å we have
observed for the related Mn(0) isonitrile complex [Mn-
(CNPh*)5SnPh3],18 but this difference is probably not
chemically significant given the wide range from 1.802-
(5) to 1.861(5) Å covered by the Mn-C bond lengths in
2. The average CtN bond length of 1.169 Å in 2 is
identical to that in [Mn(CNPh*)5SnPh3], but values
again cover a wide range from 1.156(5) to 1.180(5) Å.
F igu r e 1. Molecular structure of [Mn(CNPh*)4{C(dN-
Ph*)C(CH3)dN(Ph*)}] (35% probability ellipsoids).
Experimental Section and established that the product
is the 1,4-diazabutadien-2-yl complex [Mn(CNPh*)4-
{C(dNPh*)C(CH3)dN(Ph*)}] (2) with the molecular
structure shown in Figure 1.
The C-N-C angles of the terminal isonitrile ligands
cover a range of values from 157.9(4)° to 175.6(5)°. One
of these angles is significantly outside the range from
170° to 180° considered typical of “linear” isonitrile
ligands,9b but it is generally accepted that the variability
in bend angles in typical isonitrile complexes reflects
softness in the corresponding potential energy sur-
faces.19 The variations in C-N-C angles in 2 are,
therefore, probably a consequence of varying steric
congestion, and the ligands can be best regarded as
“electronically” linear. Thus, the most bent isonitrile
ligand is that of the C(4) isonitrile, with a C(4)-N(4)-
C(46) angle of 157.9 (4)°, and there is a close approach
between the aryl group of this ligand and the disordered
pentane of solvation.
The manganese center in 2 has a distorted octahedral
environment in which four coordination sites are oc-
cupied by terminal CNPh* ligands and the remaining
sites are occupied by a 1,4-diazabutadien-2-yl unit
formed by electrophilically induced coupling of two
isonitriles and coordinated to the metal through C(2)
and a donor bond from N(1). Three other examples of
complexes containing 1,4-diazabutadien-2-yl ligands
have been structurally characterized; the most closely
related example is the Mn complex [Mn(CO)4{C(dN-p-
tolyl)C(CH2C6H4-p-X)dN(p-tolyl)}] (X ) Cl, OMe) re-
ported by Alexander and co-workers as the product of
PdO-catalyzed double isonitrile insertion into a man-
ganese-aryl bond,11 and the earliest example is the iron
NMR Sp ectr a of [Mn (CNP h *)4{C(dNP h *)C(C-
complex [Fe(dppe)(CNPh)(I){C(dNPh)C(Me)dN(Ph)} pre-
pared by Riera et al. by addition of MeI to [Fe(dppe)-
(CNPh)3].14 Filippou et al. have reported the formation
H3)dN(P h *)}] (2). The molecular structure of 2 in
Figure 1 provides a straightforward explanation for the
initially surprising complexity of its NMR spectra, which
contains six distinct resonances in the region from δ 2.8
to 1.8 assignable to methyl groups derived from the
isonitrile ligands or the added methyl iodide. The peak
at δ 1.84 can be straightforwardly assigned to the C(7)
methyl group on the basis of its intensity, leaving
resonances at δ 2.42, 2.37, 2.34, 1.97, and 1.91 with
intensities corresponding to 4, 2, 2, 2, and 2 methyl
groups, respectively. The distinct groupings of the
chemical shifts suggests that the two higher field
resonances can be assigned to the isonitrile-derived
of a molybdenum complex [Mo(η5-C5Me5)(CO)2{C(dNR)C-
(Me)dN(Et)}] (X ) Me, Et) containing the same func-
tional group,15 and Stone’s group has observed the
formation of this functional group by alkylation of [Fe-
(CNtBu)5] to give [Fe(CNtBu)3(I){C(dNtBu)C(CH3)dN-
(CH3)}], but did not characterize the species crystallo-
graphically.16
The metric parameters for the 1,4-diazabutadien-2-
yl unit in 2 are consistent with this formulation. The
(14) Riera, V.; Ruiz, J .; J eannin, Y.; Philoche-Levisalles, M. J . Chem.
Soc., Dalton Trans. 1988, 1591.
(15) Filippou, A. C.; Gru¨nleitner, W.; Vo¨lkl, C.; Kiprof, P. J .
Organomet. Chem. 1991, 413, 181.
(16) Bassett, J .-M.; Green, M.; Howard, J . A. K.; Stone, F. G. A. J .
Chem. Soc., Dalton Trans. 1980, 1779.
(17) Allen, F. H.; Kennard, O.; Watson, D. G.; Brammer, L; Orpen,
A. G.; Taylor, R. J . Chem. Soc., Perkin Trans. II 1987, S1.
(18) Utz, T. L.; Geib, S. J .; Cooper, N. J . Manuscript in preparation.
(19) (a) Kubiak, C. P. Personal communication. (b) Hoffmann, R.
Personal communication.

Formation of [Mn(CNPh*)4{C(dNPh*)C(CH3)d(NPh*)}]
Organometallics, Vol. 16, No. 19, 1997 4113
Sch em e 2
methyl groups in the 1,4-diazabutadien-2-yl ligand,
leaving those between δ 2.5 and 2.3 to be assigned to
the terminal isonitrile ligands (c.f. δ 2.42 and 2.16 for
the methyl groups of the trans and cis isonitrile ligands,
respectively, in [Mn(CNPh*)5SnPh3]*).18
These assignments imply that two of the terminal
isonitrile ligands in 2 are chemically equivalent, and
this is consistent with the assignment of the resonance
at δ 2.42 to the C(6) and C(4) isonitriles perpendicular
to the 1,4-diazabutadien-2-yl plane. Assignments for
the 13C NMR spectra follow a similar argument.
1
The aryl region of both the H and 13C NMR spectra
contain resonances of an intensity appropriate for the
molecule as formulated, but the complex overlapping
resonances could not be meaningfully assigned to indi-
vidual aryl groups.
Gen er a lity of Alk yla tion -In d u ced Cou p lin g of
Ison itr ile Liga n d s in [K(18-C-6)][Mn (CNP h *)5]. We
examined the use of sources of electrophilic alkyl groups
other than methyl iodide to induce the coupling of
isonitrile ligands in 1- and have established that methyl
iodide is not unique in its reactivity in this system.
Methyl triflate, for example, will also react with 1- to
give 2. The yield of the reaction is, however, disap-
pointingly low, and methyl iodide remains the preferred
reagent.
We have also established that the electrophilic cou-
pling reaction can be carried out with higher alkyl
groups. Reaction of 1- with CH3CH2I in THF resulted
in a color change from blood red to bright red, and we
were able to isolate a 1,4-diazabutadien-2-yl complex
1
analogous to 2. IR and H NMR spectra suggested the
formulation of this complex as [Mn(CNPh*)4{C(dNPh*)-
ligands incorporated in the coupled product so that the
coupled product retains a higher degree of unsaturation
at carbon.
C(CH2CH3)dN(Ph*)}] (3), as confirmed by combustion
analysis.
As in the case of other 1,4-diazabutadien-2-yl com-
plexes, we propose that the ligand is formed (as shown
in Scheme 2) by insertion of an isonitrile ligand into a
metal-iminoacyl linkage, formed in situ by insertion
of an isonitrile ligand into the Mn-alkyl bond of
transient [Mn(CNPh*)5CH3] (A). The latter complex
would be the isonitrile analog of [Mn(CO)5CH3], and the
mild conditions under which 2 is formed suggests that
isonitrile/alkyl insertion in A is more rapid than car-
bonyl/alkyl insertion in [Mn(CO)5CH3], the most exten-
sively characterized substrate for migratory insertion.21
Isonitrile/alkyl insertion reactions to form iminoacyl
groups are well-established,9,10 and formation of imi-
noacyl ligands is typically assisted by adoption of the
η2-iminoacyl coordination mode10,22 so that an added
donor ligand may not be required to drive the insertion.
Insertion of an added isonitrile into a metal-iminoa-
cyl bond to give a 1,4-diazabutadien-2-yl complex has
been directly observed by Filippou in the reaction of
[Mo(η5-C5Me5)(CO)2{η2-C(dNEt)Me}] with alkyl isocya-
nides15 and has been previously proposed by Alexander
and co-workers to account for the formation of 1,4-
diazabutadien-2-yl complexes following PdO-catalyzed
substitution of p-tolyl isocyanide for carbonyl ligands
in the benzylic manganese complexes [Mn(CO)5CH2C6H5-
Attempts to extend this chemistry to include the
addition of more electrophilic alkyl halides such as
PhCH2Br met with mixed success. The addition of 1
equiv of PhCH2Br to a THF solution of 1- resulted in a
color change from blood red to orange, and the resulting
solution had an IR spectrum analogous to that of 2.
1
Crude H NMR spectra were consistent with formula-
tion of the product of this reaction as [Mn(CNPh*)4-
{C(dNPh*)C(CH2Ph)dN(Ph*)}], but attempts to isolate
pure samples were unsuccessful and precluded defini-
tive characterization.
Mech a n ism of th e Meth yla tion -In d u ced Cou -
p lin g of Ison it r ile liga n d s in NMR Sp ect r a of
[Mn (CNP h *)4{C(dNP h *)C(CH3)dN(P h *)}] (2). The
methylation-induced C-C coupling of the isonitrile
ligands in 1- to form a coordinated 1,4-diazabutadien-
2-yl presents an interesting contrast with the extensive
body of chemistry by Lippard20 on electrophile-induced
C-C coupling of isonitrile ligands in other low-valent
complexes to form coordinated alkynes. In the isoni-
trilate system methylation occurs on one of the isonitrile
carbons, while in the Lippard chemistry electrophiles
add (in steps widely separated in the mechanistic
sequence) to the nitrogen atoms of both of the isonitrile
(21) (a) Calderazzo, F.; Angew. Chem., Int. Ed. Engl. 1977, 16, 299.
(b) Kuhlmann, E. J .; Alexander, J . J . Coord. Chem. Rev. 1980, 33, 195.
(c) Wojcicki, A. Adv. Organomet. Chem. 1973, 11, 87.
(20) Carnahan, E. M.; Protasiewicz, J . D.; Lippard, S. J . Acc. Chem.
Res. 1993, 26, 90.
(22) Adams, R. D.; Chodosh, D. F. J . Am. Chem. Soc. 1977, 99, 6544.

4114 Organometallics, Vol. 16, No. 19, 1997
Utz et al.
p-X] (X ) Cl, OMe).11 It has also been inferred by
Riera14 and by Stone16 to account for the formation of
1,4-diazabutadien-2-yl complexes following alkylation of
low-valent isonitrile complexes of Fe, and a similar
mechanistic proposal was put forward earlier by Adams
to account for the reaction of [Mo(η5-C5H5)(CO)(CNMe)2]-
with methyl iodide followed by 1 equiv of I- to give
The proposal that 4 is formed by trapping an inter-
mediate in the double insertion sequence was supported
by a control experiment that eliminated the possibility
that 4 had been formed by substitution of CNtBu for a
CNPh* ligand of 2. This control involved 1H NMR
monitoring (5 min intervals) of a sample of 2 in THF-
d8 (0.023 mmol in 0.5 mL) to which 1 equiv of CNtBu
had been added. These conditions are similar in terms
of the solvent and concentration to those under which
4 had been prepared, but after 30 min at room temper-
ature about one-third of 2 had degraded without the
formation of any 4. Thermal degradation of 2 is
consistent with earlier observations on the stability of
2, and the failure to form 4 supports our suggestion that
4 is formed by addition of CNtBu to the Mn center at
some point in the double insertion sequence, most
probably after formation of B by the first insertion
reaction (Scheme 2).
[Mo(η5-C5Me5)(CO)(I){CNMe2)C(CH3)dN(Me)}].22 This
was proposed to involve formation of a 1,4-diazabuta-
dien-2-yl ligand by a sequence similar to that in Scheme
2, but in the molybdenum case a second equivalent of
methyl iodide then alkylates the ligand on nitrogen to
give the observed product. There is also a further
reaction with excess methyl iodide in our system, but
[Mn(CNPh*)5I] is the only product that we have been
able to isolate from this reaction to date.
Insertion of the second isonitrile ligand to form the
1,4-diazabutadien-2-yl ligand requires intermolecular
redistribution of isonitrile ligands, and this led to an
examination of the affect of added isonitrile on the
course of the reaction. We were disappointed to discover
that addition of 1 equiv of free CNPh* to a THF solution
of 1- before the addition of CH3I produced only a
marginal improvement (from 30 to 32%) in the yield of
2, but the importance of exogenous isonitrile was
supported by an experiment in which 1 equiv of CNtBu
was added to the THF solution of 1- before alkylation
with methyl iodide. This produced a product with
spectroscopic characteristics similar to those of 2: the
presence of methyl resonances at δ 2.05 and 1.96
indicated the formation of a 1,4-diazabutadien-2-yl
ligand by coupling of two CNPh* ligands induced by
addition of the equivalent of CH3I. The added methyl
group gives rise to a signal of appropriate intensity at
δ 1.78, while the singlet at δ 1.51 suggests that 1 (and
only one) equiv of CNtBu molecule had been incorpo-
rated into the product. This led to formulation of the
Con clu sion
The facility of isonitrile/alkyl insertion reactions in
low-valent isonitrile complexes leads to the formation
of the 1,4-diazabutadien-2-yl complex [Mn(CNPh*)4-
{C(dNPh*)C(CH3)dN(Ph*)}] when the Mn(-I) isonit-
rilate [Mn(CNPh*)5]- is alkylated with methyl iodide.
This work and earlier reports of double isonitrile inser-
tion sequences following the formation of low-valent
isonitrile/alkyl complexes through alkylation reactions
or through isonitrile substitution in carbonyl/alkyl
precursors suggests that sequences of this type will be
commonly observed as a consequence of the alkylation
of isonitrilates.
Ack n ow led gm en t. We thank the National Science
Foundation for financial support through Grant No.
CHE 9632202.
product as [Mn(CNtBu)(CNPh*)3{C(dNPh*)C(CH3)dN-
(Ph*)}] (4), as supported by combustion analysis. The
appearance of a single tBu resonance and a single
resonance for the methyl groups of the terminal isoni-
trile ligands suggests that the three isonitrile ligands
are rendered equivalent by a low-energy dynamic
process, and the choice of isomer illustrated in Scheme
1 is arbitrary.
Su p p or tin g In for m a tion Ava ila ble: Tables giving posi-
tional and thermal parameters and bond distances and angles
for [Mn(CNPh*)4{C(dNPh*)C(CH3)dN(Ph*)}] (13 pages). Or-
dering information is given on any current masthead page.
OM970287H