Ruthenium-carbene functionality bonded to dibenzotetramethyltetraaza[14]annulene: Metal-to-macrocycle ligand-induced carbene migration

Article abstract of DOI:10.1021/om980898p

This report contains the chemistry of the ruthenium-carbene functionality bonded to the dibenzotetramethyltetraaza[14]annulene dianion, tmtaa. [{Ru(tmtaa)}₂(μ-C₈H₁₂)], 1, was the most appropriate starting material, as it contains a labile olefin, which can be displaced by a number of ligands to give [Ru(tmtaa)(L)(L′)] [L = L′ = Py, 2; L = CO, L′ = thf, 3; L = Bu^tNC, L′ = thf, 4; L = L′ = Bu^tNC, 5]. Reaction of 1 with diazoalkanes led to the displacement of the olefin and gave the corresponding carbene derivatives [Ru(tmtaa)(CRR′)] [R = R′ = Ph, 6; R = Ph, R′ = H, 7; R = Ph, R′ = COOMe, 8], which have square-pyramidal structures. Complexes 7 and 8 underwent a remarkable labilization of the carbene functionality in the reaction with carbon monoxide, while 6 was only converted to the corresponding carbonyl [Ru(tmtaa)(CPh₂)(CO)], 10, by CO. The reaction of 7 with both CO and Bu^tNC led to the migration of the carbene to one of the metalladiimino rings of the ligands in 12 and 13, while the reaction of 8 with both CO and Bu^tNC enabled us to intercept the preliminary product of a free-radical-type migration of the carbene to the tmtaa ligand, with the isolation of 11 and 14. The ligand (CO or Bu^tNC)-induced migration of the CR₂ fragment to the macrocycle seemed to proceed via a carbene mechanism in the case of 7, while 8 seemed to prefer a free-radical-like pathway. This assumption was further supported by extended Hu?ckel calculations and by the reaction of 6-8 with ligands of different σ/π donor/acceptor capability. The pyridine converted 6-8 to the corresponding coordinate adducts, 15-17, while the reaction of 7 with PMe₃ led to the formation of [Ru(tmtaa)(PMe₃)₂] and stilbenes, via a plausible carbene mechanism. The reaction of 8 with PMe₃ proceeded through a free-radical pathway leading to 19, which has a structure similar to 11 and 14. The ligand-induced labilization of the metallacarbene functionality in the macrocyclic environment was analyzed using the extended Hu?ckel calculations.

Full text of DOI:10.1021/om980898p

360
Organometallics 1999, 18, 360-372
Ru th en iu m -Ca r ben e F u n ction a lity Bon d ed to
Diben zotetr a m eth yltetr a a za [14]a n n u len e:
Meta l-to-Ma cr ocycle Liga n d -In d u ced Ca r ben e Migr a tion
Alain Klose, Euro Solari, J oe¨lle Hesschenbrouck, and Carlo Floriani*
Institut de Chimie Mine´rale et Analytique, BCH, Universite´ de Lausanne,
CH-1015 Lausanne, Switzerland
Nazzareno Re
Facolta` di Farmacia, Universita` degli Studi “G. D’Annunzio”, I-66013 Chieti, Italy
Silvano Geremia and Lucio Randaccio
Dipartimento di Scienze Chimiche, Universita` di Trieste, I-34127 Trieste, Italy
Received November 2, 1998
This report contains the chemistry of the ruthenium-carbene functionality bonded to the
dibenzotetramethyltetraaza[14]annulene dianion, tmtaa. [{Ru(tmtaa)}2(µ-C8H12)], 1, was the
most appropriate starting material, as it contains a labile olefin, which can be displaced by
a number of ligands to give [Ru(tmtaa)(L)(L′)] [L ) L′ ) Py, 2; L ) CO, L′ ) thf, 3; L )
ButNC, L′ ) thf, 4; L ) L′ ) ButNC, 5]. Reaction of 1 with diazoalkanes led to the
displacement of the olefin and gave the corresponding carbene derivatives [Ru(tmtaa)(CRR′)]
[R ) R′ ) Ph, 6; R ) Ph, R′ ) H, 7; R ) Ph, R′ ) COOMe, 8], which have square-pyramidal
structures. Complexes 7 and 8 underwent a remarkable labilization of the carbene
functionality in the reaction with carbon monoxide, while 6 was only converted to the
corresponding carbonyl [Ru(tmtaa)(CPh2)(CO)], 10, by CO. The reaction of 7 with both CO
and ButNC led to the migration of the carbene to one of the metalladiimino rings of the
ligands in 12 and 13, while the reaction of 8 with both CO and ButNC enabled us to intercept
the preliminary product of a free-radical-type migration of the carbene to the tmtaa ligand,
with the isolation of 11 and 14. The ligand (CO or ButNC)-induced migration of the CR2
fragment to the macrocycle seemed to proceed via a carbene mechanism in the case of 7,
while 8 seemed to prefer a free-radical-like pathway. This assumption was further supported
by extended Hu¨ckel calculations and by the reaction of 6-8 with ligands of different σ/π
donor/acceptor capability. The pyridine converted 6-8 to the corresponding coordinate
adducts, 15-17, while the reaction of 7 with PMe3 led to the formation of [Ru(tmtaa)(PMe3)2]
and stilbenes, via a plausible carbene mechanism. The reaction of 8 with PMe3 proceeded
through a free-radical pathway leading to 19, which has a structure similar to 11 and 14.
The ligand-induced labilization of the metallacarbene functionality in the macrocyclic
environment was analyzed using the extended Hu¨ckel calculations.
In tr od u ction
methyltetraaza[14]annulene dianion, abbreviated as
tmtaa (Chart 1).2
The use of macrocycles as ancillary ligands, which
until recently has been confined to coordination chem-
istry, is now becoming more and more popular in
organometallic chemistry.1 The results so far obtained
have led to the recognition of a “macrocyclic effect”
similar to that found in coordination chemistry, though
with a different meaning. Two important directions
have been taken in the field: the first one involves the
use of early transition metals, and the second one
considers the effect of specific macrocycles. The ancillary
ligand can, of course, have a pronounced effect on the
outcome of the chemistry, with a number of ligands
being targeted because of their interesting electronic
and steric properties. One such ligand is dibenzotetra-
The tmtaa ligand has a number of major character-
istics which make its effect particularly suitable to
study. First, the geometry of the ligand is directly
related to the dn configuration of the complexed metal
and can assume either an almost square-planar or a
very pronounced saddle shape conformation.2d In the
first case, the two available reactive sites are usually
trans, whereas in the latter they have a cis relationship.
Contrary to the porphyrins and analogously to what is
found in Schiff-base chemistry, another peculiarity of
the tmtaa ligand lies in the possibility of the ligand
undergoing chemical modifications when studying the
metal reactivity. Our initial work in the area of Ru-
macrocyclic chemistry took advantage of this ligand. The
first synthesis of a Ru-tmtaa complex was reported by
* To whom correspondence should be addressed.
10.1021/om980898p CCC: $18.00 © 1999 American Chemical Society
Publication on Web 01/14/1999

Ruthenium-Carbene Functionality
Organometallics, Vol. 18, No. 3, 1999 361
Ch a r t 1
CR2] carbene complexes, whose reactivity involves both
the metal and the ancillary ligand tmtaa. Within this
context a particularly interesting aspect of the [Rud
CR2] chemistry is the ligand-induced carbene labiliza-
tion. This kind of labilization can be related to the
catalytic activity of ruthenium-carbenes inducing me-
tathesis reactions.7 Extended Hu¨ckel calculations en-
abled us to correlate the structure and electronic
properties of the Ru-carbene functionality in the two
completely different environments and its labilization
induced by a ligand as having an appropriate balance
between σ-donating and π-accepting properties. A pre-
liminary account of the reaction of [Ru(tmtaa)CR2] with
CO has been communicated.8
Goedken, in a preliminary form and described [Ru-
(tmtaa)]2.3 The isolation of well-defined monomeric
forms was later reported by Cotton, who prepared [Ru-
(tmtaa)(PMePh2)2],4 and subsequently the similar [Ru-
(Me4tmtaa)(PPh3)2] complex was reported.5 The [Ru-
(tmtaa)] fragment can provide a particularly useful
entry into the organometallic chemistry of ruthenium,
by stressing the differences in the chemical behavior of
the metal depending on the nature of the macrocyclic
ligand. As a matter of fact, the organometallic chemistry
of the Ru-macrocycle has been confined so far almost
exclusively to porphyrin ligands.6 We report here the
synthesis of a starting material that can be considered
as a particularly suitable source of the [Ru(tmtaa)]
fragment along with the synthesis of the [Ru(tmtaa)-
Exp er im en ta l Section
Gen er a l P r oced u r e. All reactions were carried out under
an atmosphere of purified nitrogen. Solvents were dried and
distilled before use by standard methods. 1H NMR and IR
spectra were recorded on AC-200, DPX-400 Bruker, and
Perkin-Elmer FT 1600 instruments, respectively. The synthe-
ses of [Ru(COD)Cl2]2,9 tmtaaH2,2d Ph2CN2,10 PhHCN2,11 Ph-
(COOMe)CN2,12 have been carried out according to the litera-
ture.
Syn th esis of 1. To a THF solution (550 mL) of tmtaaH2
(13.7 g, 39.7 mmol) was added dropwise a solution of ButLi in
n-hexane (1.64 M, 80.0 mmol). After stirring for 3 h, degassed
[(COD)RuCl2] (11.1 g, 39.7 mmol) was added, and the red
solution stirred for a further 20 h. The resulting brown
microcrystalline product was filtered, washed with THF (30
mL), and dried in vacuo (17.5 g, 82%). Potentiometric analysis
showed that the product did not contain any chloride ion. Anal.
Calcd for [{Ru(tmtaa)}2(µ-C8H12)]‚thf, C56H64N8ORu2: C, 63.48;
(1) For some general references see: Collman, J . P.; Hegedus, L.
S.; Norton, J . R.; Finke, R. G. Principles and Applications of Organ-
otransition Metal Chemistry; University Science Books: Mill Valley,
CA, 1987. For porphyrins, see: Brand, H.; Arnold, J . Angew. Chem.,
Int. Ed. Engl. 1994, 33, 95. Brand, H.; Arnold, J . Organometallics 1993,
12, 3655. Kim, H.-J .; Whang, D.; Kim K.; Do, Y. Inorg. Chem. 1993,
32, 360. Arnold, J .; J ohnson, S. E.; Knobler C. B.; Hawthorne, M. F. J .
Am. Chem. Soc. 1992, 114, 3996. Brand H.; Arnold, J . J . Am. Chem.
Soc. 1992, 114, 2266. Brand, H.; Arnold, J . Coord. Chem. Rev. 1995,
140, 137. Aida, T.; Inoue, S. Acc. Chem. Res. 1996, 29, 39, and ref 6.
For meso-octaalkylporphyrinogen, see: J acoby, D.; Floriani, C.; Chiesi-
Villa, A.; Rizzoli, C. J . Chem. Soc., Chem. Commun. 1991, 790. J acoby,
D.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C. J . Am. Chem. Soc. 1993,
115, 3595. J acoby, D.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C. J . Am.
Chem. Soc. 1993, 115, 7025. Rosa, A.; Ricciardi, G.; Rosi, M.; Sgamel-
lotti, A.; Floriani, C. J . Chem. Soc., Dalton Trans. 1993, 3759. Solari,
E.; Musso, F.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C. J . Chem. Soc.,
Dalton Trans. 1994, 2015. J acoby, D.; Isoz, S.; Floriani, C.; Chiesi-
Villa, A.; Rizzoli, C. J . Am. Chem. Soc. 1995, 117, 2793. J acoby, D.;
Isoz, S.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C. J . Am. Chem. Soc.
1995, 117, 2085. For calix[4]arenes, see: Giannini, L.; Solari, E.;
Zanotti-Gerosa, A.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C. Angew.
Chem., Int. Ed. Engl. 1996, 35, 85 and 2825; 1997, 36, 753. Castellano,
B.; Zanotti-Gerosa, A.; Solari, E.; Floriani, C.; Chiesi-Villa, A.; Rizzoli,
C. Organometallics 1996, 15, 4894. Giannini, L.; Caselli, A.; Solari,
E.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C.; Re, N.; Sgamellotti, A. J .
Am. Chem. Soc. 1997, 119, 9198 and 9709. Caselli, A.; Giannini, L.;
Solari, E.; Floriani, C.; Re, N.; Chiesi-Villa, A.; Rizzoli, C. Organome-
tallics 1997, 16, 5457. Zanotti-Gerosa, A.; Solari, E.; Giannini, L.;
Floriani, C.; Chiesi-Villa, A.; Rizzoli, C. J . Am. Chem. Soc. 1998, 120,
437. Giannini, L.; Solari, E.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C.
J . Am. Chem. Soc. 1998, 120, 823.
1
H, 6.04; N, 10.56. Found: C, 63.10; H, 6.44; N, 9.58. H NMR
(C5D5N, 200 MHz, 298 K, ppm): δ 6.77-6.72 (m, 4H, Ar);
6.32-6.27 (m, 4H, Ar); 5.56 (s, 2H, COD-CH); 4.04 (s, 2H,
CH); 3.64 (m, 2H, THF); 2.25 (s, 4H, COD-CH2); 1.95 (s, 12H,
CH3); 1.59 (m, 2H, THF).
Syn th esis of 2. To a toluene suspension (100 mL) of 1‚thf
(0.93 g, 0.87 mmol) was added pyridine (0.35 mL, 4.35 mL).
The mixture was stirred overnight to give a red solution, which
was then filtered. Solvent was removed in vacuo to 15 mL and
n-hexane (30 mL) added. The red product was filtered, washed
with n-hexane (30 mL), and dried in vacuo (0.75 g, 72%). Anal.
Calcd for [Ru(tmtaa)(Py)2]‚C7H8, C39H40N6Ru: C, 67.51; H,
5.81; N, 12.11. Found: C, 66.95; H, 6.03; N, 12.17. 1H NMR
(C6D6, 200 MHz, 298 K, ppm): δ 9.58 (s, 4H, py); 7.09-6.24
(m, 19H, Ar); 4.01 (s, 2H, CH); 2.10 (s, 3H, toluene); 1.89 (s,
12H, CH3).
Syn th esis of 3. A brown THF suspension (150 mL) of 1‚
thf (2.1 g, 1.97 mmol) was cooled (-20 °C) and then saturated
with CO to give a solution which was kept under CO overnight
and then concentrated to 10 mL. n-Hexane (20 mL) was added,
and the crystalline product filtered and dried in vacuo (1.36
(2) Some leading references in the use of [tmtaa]2- as ancillary
ligand in the organometallic chemistry of the early transition metals
are: (a) Goedken, V. L.; Ladd, J . A. J . Chem. Soc., Chem. Commun.
1981, 910; 1982, 142. (b) Floriani, C.; Ciurli, S.; Chiesi-Villa, A.;
Guastini, C. Angew. Chem., Int. Ed. Engl. 1987, 26, 70. (c) Solari, E.;
De Angelis, S.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C. Inorg. Chem.
1992, 31, 96. (d) De Angelis, S.; Solari, E.; Gallo, E.; Floriani, C.; Chiesi-
Villa, A.; Rizzoli, C. Inorg. Chem. 1992, 31, 2520. (e) Giannini, L.;
Solari, E.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C. Angew. Chem., Int.
Ed. Engl. 1994, 33, 2204. (f) Giannini, L.; Solari, E.; De Angelis, S.;
Ward, T. R.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C. J . Am. Chem.
Soc. 1995, 117, 5801. (g) Black, D. G.; Swenson, D. C.; J ordan, R. F.
Organometallics 1995, 14, 3539. (h) Blake, A. J .; Mountford, P.;
Nikonov, G. I.; Swallow, D. Chem. Commun. 1996, 1835. (i) Schumann,
H. Inorg. Chem. 1996, 35, 1808. (j) Nikonov, G. I.; Blake, A. J .;
Mountford, P. Inorg. Chem. 1997, 36, 1107. Black, D. G.; J ordan, R.
F.; Rogers, R. D. Inorg. Chem. 1997, 36, 103. Martin, A.; Uhrhammer,
R.; Gardner, T. G.; J ordan, R. F. Organometallics 1998, 17, 382.
Mountford, P. Chem. Soc. Rev. 1998, 27, 105.
(6) Collman, J . P.; Barnes, C. E.; Swepston, P. N.; Ibers, J . A. J .
Am. Chem. Soc. 1984, 106, 3500. Collman, J . P.; Brothers, P. J .; Mc-
Elwee-White, L.; Rose, E.; Wright, L. J . J . Am. Chem. Soc. 1985, 107,
4570. Collman, J . P.; Brothers, P. J .; Mc-Elwee-White, L.; Rose, E. J .
Am. Chem. Soc. 1985, 107, 6110.
(7) (a) Grubbs, R. H.; Miller, S. J .; Fu, G. C. Acc. Chem. Res. 1995,
28, 446. (b) Nguyen, S. T.; Grubbs, R. H.; Ziller, J . W. J . Am. Chem.
Soc. 1993, 115, 9858. (c) Miller, S. J .; Blackwell, H. E.; Grubbs, R. H.
J . Am. Chem. Soc. 1996, 118, 9606. (d) Mohr, B.; Linn, D. M.; Grubbs,
R. H. Organometallics 1996, 15, 4317.
(8) Klose, A.; Solari, E.; Floriani, C.; Geremia, S.; Randaccio, L.
Angew. Chem., Int. Ed. Engl. 1998, 37, 148.
(9) Powell, J .; Shaw, B. L. J . Chem. Soc. (A) 1968, 159.
(10) Smith, L. I.; Howard, K. L. Organic Syntheses; Wiley: New
York, 1955; Vol. 3, p 351.
(3) Warren, L. F.; Goedken, V. L. J . Chem. Soc., Chem. Commun.
1978, 909.
(4) Cotton, F. A.; Czuchajowska, J . Polyhedron 1990, 9, 1221.
(5) Luo, L.; Stevens, E. D.; Nolan, S. P. Inorg. Chem. 1996, 35, 252.
(11) Yates, P.; Shapiro, L. J . Org. Chem. 1958, 23, 759.
(12) Ciganek, E. J . J . Org. Chem. 1970, 35, 862.

362 Organometallics, Vol. 18, No. 3, 1999
Klose et al.
g, 63%). Anal. Calcd for [Ru(tmtaa)(CO)(thf)], C27H30N4O2Ru:
C, 59.65; H, 5.56; N, 10.31. Found: C, 59.58; H, 5.34; N, 10.27.
1H NMR (C6D6, 200 MHz, 298 K, ppm): δ 6.75-6.70 (m, 4H,
Ar); 6.54-6.49 (m, 4H, Ar); 4.43 (s, 2H, CH); 3.58 (m, 4H,
THF); 1.96 (s, 12H, CH3); 1.33 (m, 4H, THF). 13C NMR (C6D6,
50.3 MHz, 298 K, ppm): δ 217.4 (CO), 156.4, 149.6, 122.1,
121.4, 68.2, 25.2, 24.9.
Syn th esis of 4. To a brown THF suspension (100 mL) of
1‚thf (1.44 g, 1.34 mmol) was added dropwise a THF solution
(30 mL) of ButNC (0.24 g, 2.8 mmol). The color slowly became
dark green, and a new microcrystalline product precipitated.
The reaction was stirred overnight and then concentrated to
30 mL. n-Hexane (15 mL) was added, and the product filtered
and dried in vacuo (0.82 g, 51%). Anal. Calcd for [Ru(tmtaa)-
(ButNC)(thf)], C31H39N5ORu: C, 62.19; H, 6.57; N, 11.70.
Found: C, 62.03; H, 6.70; N, 11.93. 1H NMR (C5D5N, 200 MHz,
298 K, ppm): δ 6.84-6.79 (m, 4H, Ar); 6.55-6.52 (m, 4H, Ar);
4.00 (s, 2H, CH); 3.63 (m, 4H, THF); 1.89 (s, 12H, CH3); 1.59
(m, 4H, THF); 1.23 (s, 9H, But). 13C NMR (C5D5N, 50.3 MHz,
298 K, ppm): δ 194.0 (CN), 153.9, 151.5, 121.5, 120.9, 111.7,
67.8, 32.5, 25.8, 24.7.
Syn th esis of 5. To a THF suspension (120 mL) of 1‚thf (1.99
g, 1.87 mmol) was added dropwise a THF solution (50 mL) of
ButNC (0.66 g, 8.0 mmol). Complete solubilization was ob-
served, and the solution stirred overnight. The volume was
decreased in vacuo to 10 mL, and n-hexane (25 mL) added.
The crystalline product was filtered, then washed with n-
hexane (20 mL) and dried in vacuo (1.35 g, 59%). Anal. Calcd
for [Ru(tmtaa)(ButNC)2], C32H40N6Ru: C, 63.03; H, 6.61; N,
13.78. Found: C, 63.10; H, 6.75; N, 13.53. 1H NMR (C6D6, 200
MHz, 298 K, ppm): δ 6.67-6.63 (m, 4H, Ar); 6.39-6.34 (m,
4H, Ar); 4.22 (s, 2H, CH); 1.88 (s, 12H, CH3); 1.11 (s, 18H,
But). 13C NMR (C6D6, 50.3 MHz, 298 K, ppm): δ 164.7 (CN).
Crystals for X-ray analysis were obtained from toluene and
analyzed as solvated forms.
the resulting microcrystalline product filtered and dried in
vacuo (1.09 g, 60%). Anal. Calcd for [Ru(tmtaa){C(Ph)-
(COOMe)}], C31H30N4O2Ru: C, 62.93; H, 5.11; N, 9.47.
1
Found: C, 62.68; H, 5.17; N, 9.63. H NMR (C6D6, 200 MHz,
298 K, ppm): δ 6.91-6.83 (m, 9H, Ar); 6.64-6.60 (m, 4H, Ar);
4.91 (s, 2H, CH); 3.04 (s, 3H, CH3 COO); 2.20 (s, 12H).13C NMR
(C6D6, 100.6 MHz, 298 K, ppm): δ 279.2 (C carbene), 178.3,
156.1, 153.5, 149.7, 127.2, 126.1, 122.1, 121.8, 120.9, 110.8,
50.4, 25.4.
Syn th esis of 9. To a cooled (-40 °C) brown THF suspension
(140 mL) of 1‚thf (1.92 g, 1.79 mmol) was added via seringe
(o-Me3Si)PhNC (0.69 g, 3.59 mmol). A sudden color change to
dark red was observed. The suspension was allowed to warm
to room temperature and stirred overnight to give a solution.
The solvent was removed to 5 mL, and n-hexane (40 mL)
added. The crystalline solid was filtered and dried in vacuo
(1.88 g, 84%). The solid did not lose THF in vacuo. Anal. Calcd
for [Ru(tmtaa)(o-Me3SiOC6H4NC)]‚thf, C36H43N5O2SiRu: C,
1
61.17; H, 6.13; N, 9.91. Found: C, 60.99; H, 6.09; N, 9.87. H
NMR (C6D6, 200 MHz, 298 K, ppm): δ 6.95-6.53 (m, 12H,
Ar); 4.47 (s, 2H, CH); 3.66 (m, 4H, THF); 2.02 (s, 12H, CH3);
1.40 (m, 4H, THF); 0.21 (s, 9H, Me3). 13C NMR (C6D6, 100.6
MHz, 298 K, ppm): δ 208.8 (CN), 155.4, 150.5, 129.6, 125.2,
122.3, 121.7, 121.6, 121.1, 110.7, 68.1, 25.5, 24.8.
Syn th esis of 10. A THF suspension (100 mL) of 6‚thf (1.20
g, 1.76 mmol) was cooled to -30 °C and then saturated with
CO. No change of color was observed. The suspension was
allowed to warm to room temperature and stirred for 5 h to
give a solution. Solvent was removed to dryness, and the
product treated with n-hexane (20 mL). The resulting suspen-
sion was filtered, and the product dried in vacuo (0.68 g, 61%).
Anal. Calcd for [Ru(tmtaa)(CPh2)(CO)], C36H32N4ORu: C,
67.80; H, 5.06; N, 8.78. Found: C, 67.90; H, 5.28; N, 9.20. IR
(Nujol, νmax/cm-1): 1906 (m, CO).1H NMR (C6D6, 200 MHz, 298
K, ppm): δ 6.92-6.89 (m, 4H, Ar); 6.74-6.70 (m, 4H, Ar); 6.45
(m, 10H, Ph); 4.92 (s, 2H, CH); 2.13 (s, 12H, CH3).13C NMR
(C6D6, 100.6 MHz, 298 K, ppm): δ 291.7 (C carbene), 270.9
(CO).
Syn th esis of 6. To a THF suspension (150 mL) of 1‚thf (3.77
g, 3.53 mmol) was added a THF solution (50 mL) of diphenyl-
diazomethane (1.38 g, 7.10 mmol). The mixture slowly became
soluble with the concomitant evolution of nitrogen gas. The
solution was stirred for 36 h and then concentrated to 10 mL.
n-Hexane was added (30 mL), and the microcrystalline mate-
rial filtered and dried in vacuo (3.55 g, 74%). Crystals suitable
for X-ray analysis were grown in THF/n-hexane. Anal. Calcd
for [Ru(tmtaa)(CPh2)]‚thf, C39H40N4ORu: C, 68.70; H, 5.91; N,
Syn th esis of 11. An orange THF solution (100 mL) of 8
(0.58 g, 0.98 mmol) was cooled (0 °C) and then saturated with
CO. The solution immediately became red and was then kept
overnight under CO. The solvent was removed in vacuo, the
product was then treated with n-hexane (30 mL) and filtered,
and the resulting solid was dried in vacuo (0.39 g, 64%). Anal.
Calcd for 11, C32H30N4O3Ru: C, 62.02; H, 4.88; N, 9.04.
Found: C, 61.50; H, 5.10; N, 8.92. IR (Nujol, νmax/cm-1): 1905
1
8.22. Found: C, 68.78; H, 5.99; N, 8.52. H NMR (C6D6, 200
MHz, 298 K, ppm): δ 6.92-6.88 (m, 4H, Ar); 6.73-6.69 (m,
4H, Ar); 6.45 (m, 10H, Ph); 4.91 (s, 2H, CH); 3.56 (m, 4H, THF);
2.13 (s, 12H, CH3); 1.40 (m, 4H, THF).13C NMR (C6D6, 50.3
MHz, 298 K, ppm): δ 291.8 (C carbene). THF was kept even
when the solid was dried in vacuo for a long time.
Syn th esis of 7. To a cooled (-30 °C) THF suspension (150
mL) of 1‚thf (2.09 g, 1.96 mmol) was added phenyldiaz-
omethane (0.47 g, 3.92 mmol). The reaction occurred im-
mediately with the concomitant evolution of nitrogen gas. The
solution was allowed to warm to room temperature and stirred
overnight. Solvent was removed to 10 mL, and n-hexane (25
mL) added. The crystalline product was filtered and dried in
vacuo (1.34 g, 64%). Anal. Calcd for [Ru(tmtaa)(CHPh)],
1
(s, CO), 1732 (m, COO), 1628 (m). H NMR (C6D6, 400 MHz,
298 K, ppm): δ 7.87-6.51 (m, 13H, Ar); 4.65 (s, 1H, HCdC);
4.48 (s, 1H, CH); 3.59 (s, 3H, OCH3); 2.01 (s, 6H, CH3); 1.88
(s, 6H, CH3). 13C NMR (C6D6, 100.6 MHz, 298 K, ppm): δ 211.9
(CO). Crystals suitable for X-ray analysis were grown in
toluene/n-hexane (1/1) and contained toluene of crystallization.
Syn th esis of 12. An orange toluene suspension (100 mL)
of 7 (0.93 g, 1.74 mmol) was cooled (-35 °C) and then saturated
with CO. The suspension turned green and slowly, on warming
to room temperature, dissolved to give a red solution. After 2
h stirring, the solvent was removed to 10 mL, and n-hexane
added (20 mL). The crystalline product was filtered and dried
in vacuo (0.73 g, 71%). Anal. Calcd for 12, C31H28N4O2Ru: C,
63.15; H, 4.79; N, 9.50. Found: C, 63.08; H, 4.53; N, 9.36. IR
(Nujol, νmax/cm-1): 2016 (s, CO), 1948 (s, CO). 1H NMR (C6D6,
400 MHz, 298 K, ppm): δ 7.44-6.61 (m, 13H, Ar); 5.20 (s, 1H,
HCdC); 3.18 (d, J ) 14.7 Hz, 1H, CH2); 2.52 (s, 3H, CH3); 2.48
(d, J ) 14.7 Hz, 1H, CH2); 2.29 (s, 3H, CH3); 2.19 (s, 3H, CH3);
1.39 (s, 3H, CH3). 13C NMR (C6D6, 100.6 MHz, 298 K, ppm):
δ 199.8, 197.5. Crystals suitable for X-ray analysis were grown
in toluene/n-hexane (1/1) and contained toluene of crystalliza-
tion.
C
29H28N4Ru: C, 65.27; H, 5.29; N, 10.50. Found: C, 64.83; H,
5.34; N, 10.28. 1H NMR (CD2Cl2, 400 MHz, 298 K, ppm): δ
17.1 (s, 1H, CH carbene); 7.22-6.79 (m, 13H, Ar); 4.90 (s, 2H,
CH); 2.44 (s, 12H, CH3). 13C NMR (CD2Cl2, 100.6 MHz, 298 K,
ppm): δ 156.1, 154.9, 150.2, 128.9, 126.9, 125.9, 122.6, 122.0,
109.4, 25.4.
Syn th esis of 8. To a cooled (-20 °C) THF suspension (150
mL) of 1‚thf (1.65 g, 1.54 mmol) was added diazomethylphe-
nylglyoxylate (0.60 g, 3.40 mmol). The suspension was allowed
to warm to room temperature and stirred overnight. The
mixture slowly became soluble with the concomitant evolution
of nitrogen gas. The solution was filtered and the solvent
reduced to 15 mL. n-Hexane (20 mL) was added dropwise, and
Syn th esis of 13. To a cooled (-20 °C) stirred red toluene
suspension (100 mL) of 7 (1.27 g, 2.39 mmol) was added a
toluene solution (40 mL) of ButNC (0.40 g, 4.78 mmol).

Ruthenium-Carbene Functionality
Organometallics, Vol. 18, No. 3, 1999 363
Warming to room temperature and stirring for 3 h gave a
green solution. The solvent was removed to 5 mL, n-hexane
(30 mL) was added, and the solution was left to stand for 1 h.
The resulting green crystalline solid was collected by filtration
and dried in vacuo (0.89 g, 54%). Anal. Calcd for 13, C39H46N6-
Ru: C, 66.93; H, 6.62; N, 12.01. Found: C, 66.01; H, 6.52; N,
11.95. IR (Nujol, νmax/cm-1): 2095 (s, CN), 1595 (s), 1565 (s).1H
NMR (C6D6, 400 MHz, 298 K, ppm): δ 7.61-6.43 (m, 13H,
Ar); 5.69 (d, J ) 13.1 Hz, 1H, CH2); 5.04 (s, 1H, HCdC); 3.43
(d, J ) 13.1 Hz, 1H, CH2); 2.56 (s, 3H, CH3); 2.54 (s, 3H, CH3);
2.45 (s, 3H, CH3); 1.99 (s, 3H, CH3); 0.96 (s, 9H, But); 0.82 (s,
9H, But). 13C NMR (C6D6, 100.6 MHz, 298 K, ppm): δ 173.9,
160.4.
Syn th esis of 14. To a cooled (-20 °C) red toluene suspen-
sion (100 mL) of 8 (1.04 g, 1.75 mmol) was added a toluene
solution (30 mL) of ButNC (0.15 g, 1.75 mmol). Warming to
room temperature and stirring for 24 h gave a green solution.
The solvent was removed to 10 mL, and n-hexane (20 mL)
added. The microcrystalline solid was then filtered and dried
in vacuo (0.74 g, 63%). Anal. Calcd for 14, C36H39N5O2Ru: C,
64.08; H, 5.83; N, 10.38. Found: C, 64.97; H, 5.91; N, 9.32. IR
(Nujol, νmax/cm-1): 1935 (s, CN), 1628 (s, COO).1H NMR (C6D6,
400 MHz, 298 K, ppm): δ 7.93-6.49 (m, 13H, Ar); 4.70 (s, 1H,
HCdC); 4.58 (s, 1H, CH); 3.69 (s, 3H, OCH3); 2.09 (s, 6H, CH3);
1.95 (s, 6H, CH3), 0.86 (s, 9H, But).13C NMR (C6D6, 100.6 MHz,
298 K, ppm): δ 190.7 (CN).
Syn th esis of 15. To a THF (-10 °C) suspension of 6‚thf
(0.63 g, 0.92 mmol) was added pyridine (0.10 mL, 1.2 mmol),
and the reaction mixtured stirred overnight to give a red
solution. The solution was filtered and solvent removed to 10
mL in vacuo. n-Hexane was added, and the microcrystalline
product filtered and dried in vacuo (0.41 g, 57%). Anal. Calcd
for C40H37N5Ru: C, 69.75; H, 5.41; N, 10.17. Found: C, 68.89;
H, 6.02; N, 9.63. 1H NMR (C6D6, 400 MHz, 298 K, ppm): δ
8.75 (d, 2H, J ) 4.4 Hz, py), 7.11-6.91 (m, 11H, Ar+py), 6.39-
6.35 (m, 10H, Ph), 4.53 (s, 2H, CH), 1.98 (s, 12H, CH3). 13C
NMR (C6D6, 100.6 MHz, 298 K, ppm): δ 300.6 (C carbene),
162.5.
stilbene (86%, 14%). Anal. Calcd for [Ru(tmtaa)(PMe3)2],
C
28H40N4P2Ru: C, 56.46; H, 6.77; N, 9.41. Found: C, 55.59;
H, 7.01; N, 9.30. 1H NMR (C6D6, 200 MHz, 298 K, ppm): δ
6.75-6.70 (m, 4H, Ar); 6.41-6.36(m, 4H, Ar); 4.11 (s, 2H, CH);
1.87 (s, 12H, CH3); 1.37 (t, 18H, Me3). 31P[1H] NMR (C6D6, 81
MHz, 298 K, ppm): δ 4.02.
Syn th esis of 19. To a cooled (-20 °C) toluene suspension
of 8 (0.46 g, 0.78 mmol) was added a THF solution of PMe3
(0.06 g, 0.78 mmol). The suspension turned yellow and, on
warming to room temperature, dissolved to give a green
solution. Solvent was removed to dryness, and n-hexane (30
mL) added. The green precipitate was filtered and dried in
vacuo (0.25 g, 48%). The product was recrystallized in toluene/
n-hexane. Anal. Calcd for 19, C34H39N4O2P1Ru: C, 61.16; H,
5.89; N, 8.39. Found: C, 60.42; H, 6.18; N, 8.24. IR (Nujol,
ν
max/cm-1): 1728 (s, COO), 1603 (m).1H NMR (C6D6, 400 MHz,
298 K, ppm): δ 7.78-6.40 (m, 13H, Ar); 5.13 (s, 1H, HCdC);
4.23 (s, 1H, CH); 3.43 (s, 3H, OCH3); 2.10 (s, 6H, CH3); 2.02
(s, 6H, CH3), 1.11 (s, 9H, Me3).31P[1H] NMR (C6D6, 81 MHz,
298 K, ppm): δ 0.54.
X-r a y Cr ysta llogr a p h y for Com p lexes 5, 6, 11, a n d 12
in Th eir Solva ted F or m . Crystals of 5, 6, 11, and 12 were
mounted in glass capillaries and sealed under nitrogen.
Intensity data for all four complexes were collected on a Rigaku
AFC7 single-crystal diffractometer by using graphite-mono-
chromated Mo KR radiation (λ ) 0.7107 Å). Crystal data are
reported in Table 1. The intensities were corrected for Lorentz
and polarization factors. No absorption correction was applied.
The structures were solved by conventional Patterson and
Fourier methods and refined through full-matrix least-squares
methods. The non-hydrogen atoms were treated anisotropi-
cally. The hydrogen atoms, located on positive regions of the
difference Fourier maps, were added as fixed contributions at
their calculated positions. In both 5 and 11 the Fourier maps
showed that one molecule of toluene was located around an
inversion center, with half-occupancy of the methyl group.
Complex neutral-atom scattering factors, including anomalous
dispersion terms for all non-H atoms, were taken from
International Tables for X-ray Crystallography.13 Calculations
were carried out by using SHELX93.14 Final non-H positional
parameters, anisotropic thermal parameters, H atom coordi-
nates, and tables of all bond lengths and angles are available
as Supporting Information.15
Syn th esis of 16. To a cooled (-10 °C) THF solution of 7
(0.73 g, 1.4 mmol) was added pyridine (0.22 mL, 2.7 mmol).
The solution was allowed to warm to room temperature and
stirred overnight. Solvent was removed in vacuo to 10 mL, and
n-hexane (20 mL) added. The purple microcrystalline solid was
filtered and dried in vacuo (0.45 g, 54%). Anal. Calcd for [Ru-
(tmtaa)(CHPh)(Py)], C34H33N5Ru: C, 66.65; H, 5.43; N, 11.43.
Resu lts a n d Discu ssion
1
Found: C, 65.81; H, 5.01; N, 10.95. H NMR (C6D6, 400 MHz,
298 K, ppm): δ 18.3 (s, 1H, CH carbene); 8.73 (s, 2H, py); 8.12
(d, J ) 7.3 Hz, 1H, py); 7.27-6.53 (m, 15H, Ar+py); 4.15 (s,
2H, CH); 1.92 (s, 12H, CH3). 13C NMR (C6D6, 100.6 MHz, 298
K, ppm): δ 296.3 (CH carbene).
(a ) Ru th en iu m -tm ta a Der iva tives. For the pur-
poses of this study we found [{Ru(tmtaa)}2(µ-C8H12)],
1, to be the most appropriate starting material in that
its preparation is straightforward, high yielding, and
involves the labile olefin ligand. The synthesis of 1 and
its conversion to other [Ru(tmtaa)] derivatives is out-
lined in Scheme 1.
The NMR characterization of 1 was not possible in
noncoordinating solvents due to its insoluble nature,
whereas spectra recorded in pyridine actually cor-
responded to that of 2. Complexes 2-5 display a
common pattern in the 1H NMR spectrum with a singlet
for the meso-imino protons and a singlet for the four
methyls, which are also the most sensitive to confor-
mational changes of the tmtaa ligand. The C-O and
C-N stretching vibrations are diagnostic of the electron
density at the metal. Surprisingly low C-O [1904 cm-1
in 3] and C-N [1920 cm-1 in 4 vs 2134 cm-1 in free
Syn th esis of 17. To a cooled (-20 °C) THF solution of 8
(0.84 g, 1.41 mmol) was added pyridine (0.12 mL, 1.4 mmol).
The solution was allowed to warm to room temperature and
then stirred for 5 h. The solvent was then removed in vacuo
to 10 mL, and n-hexane (15 mL) added. The orange product
was filtered and dried in vacuo (0.42 g, 44.4%). Anal. Calcd
for [Ru(tmtaa){C(Ph)(COOMe)}(Py)], C36H35N5O2Ru: C, 64.46;
H, 5.26; N, 10.44. Found: C, 64.24; H, 5.33; N, 10.32. 1H NMR
(C6D6, 400 MHz, 298 K, ppm): δ 8.88 (m, 2H, py); 8.03 (d, J )
7.2 Hz, 1H, py); 7.26-7.15 (m, 4H, Ar); 6.87-6.54 (m, 11H,
Ar+py); 4.39 (s, 2H, CH); 3.51 (s, 3H, MeO); 2.08 (s, 12H, CH3).
13C NMR (C6D6, 100.6 MHz, 298 K, ppm): δ 285.6 (C carbene).
Syn th esis of 18. To a cooled (-30 °C) stirred red toluene
suspension (150 mL) of 7 (1.35 g, 2.54 mmol) was added a thf
solution (30 mL) of PMe3 (0.39 g, 5.08 mmol). The suspension
was allowed to warm to room temperature and stirred over-
night. The resulting green solution was concentrated to 20 mL,
and n-hexane (30 mL) added. The green microcrystalline
product was filtered and dried in vacuo (0.87 g, 58%). This
complex was analyzed as [Ru(tmtaa)(PMe3)2]. A GC analysis
of the mother liquor showed the presence of cis- and trans-
(13) International Tables for X-ray Crystallography; Kynoch Press:
Birmingham, England, 1974; Vol. IV.
(14) Sheldrick, G. M. SHELXL-93, Program for Crystal Structure
Refinement; University of Go¨ttingen, Go¨ttingen, Germany, 1993.
(15) See paragraph at the end regarding Supporting Information.

364 Organometallics, Vol. 18, No. 3, 1999
Ta ble 1. Cr ysta l Da ta a n d Str u ctu r e Refin em en t for 5, 6, 11, a n d 12
Klose et al.
5
6
11
12
chem formula
fw
temp, K
cryst syst
space group
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
C
32H40N6Ru‚0.5C7H8
C35H32N4Ru‚C4H8O
681.82
143(2)
triclinic
P1h
11.414(14)
14.297(12)
11.332(8)
108.77(6)
104.29(10)
105.25(11)
1574(3)
2
C32H30N4O3Ru‚1.5C7H8
C31H28N4O2Ru‚C7H8
681.78
293(2)
triclinic
P1h
10.617(5)
19.436(10)
8.378(3)
90.34(4)
104.24(3)
80.99(4)
1654.1(13)
2
655.84
143(2)
triclinic
P1h
12.481(4)
13.145(3)
10.587(3)
96.87(2)
101.76(2)
103.65(2)
1626.5(8)
2
757.37
143(2)
monoclinic
P21/c
11.269(4)
9.445(2)
33.854(12)
90
91.63(3)
90
3602(2)
4
Z
D
calc, g/cm3
1.339
0.516
686
1.439
0.537
708
1.397
0.481
1570
1.369
0.513
704
µ, mm-1
F(000)
indep refls
5839
0.993
0.039
0.097
5843
1.030
0.088
0.222
4987
1.896
0.036
0.112
7245
1.017
0.046
0.107
GOFa
Rb [I > 2σ(I)]
wR2c [I > 2σ(I)]
GOF ) [∑w(|Fo| - |Fc|)2/(no. obser - no. variab)]. R ) ∑|∆F|/∑|Fo|. c wR2 ) [∑(w∆F2)2/∑(wFo2)2]1/2
.
a
b
Sch em e 1
F igu r e 1. ORTEP drawing (thermal ellipsoid 50% prob-
ability) of complex 5.
ment is almost exclusively trans, as confirmed by X-ray
analyses. Due to the particular focus of this paper on
the Ru-C multiple bond, only the X-ray analysis of 5
will be reported. The structure of 5 is displayed in
Figure 1, with a list of the corresponding selected
parameters in Table 2. Although the metal is hexaco-
ordinate, unlike the phosphine derivatives [Ru(tmtaa)-
(PR3)2],4,5 the ligand has a slight saddle shape confor-
mation, with the arene substituents tilted up in the C23
direction and the diiminato rings on the opposite side,
the dihedral angles with the N4 plane being 18.0(1)°,
22.2(3)°, and 12.3(3)°, 19.8(1)°, respectively. The metal
out-of-plane distance [0.026(2) Å] is not particularly
informative in the case of hexacoordinate [M(tmtaa)L2]
complexes. The structural parameters related to the
[Ru(tmtaa)] fragment show the usual trend.2 A signifi-
cant difference has been observed between Ru-C23
[1.980(4) Å] and Ru-C28 [2.013(4) Å] according to a
different steric environment for the two isonitriles. Such
Ru-C bond distances are significantly longer than those
in the analogous porphyrin complex [Ru(TPP)(ButNC)2]
[Ru-Cav, 1.901(3) Å].17 The deviation of the Ru-C-N
(isonitrile) fragment from linearity occurs almost nor-
ButNC] bands were observed for complexes 3 and 4, and
this is indicative of high electron density and an efficient
π-back-bonding to the ligand. The displacement of the
equatorial thf in 3 and 4 by a further molecule of ligand
was successful only for 4. Unlike ruthenium-porphyrin
chemistry, we did not observe the formation of a
dicarbonyl like [Ru(TPP)(CO)2], though in the latter case
the second CO is extremely labile and was lost even
under a N2 atmosphere.16 The obtention of 5 [νCN, 2091
cm-1] is related to the greater σ-donating and lower
π-acidic nature of the isocyanide ligand. In all [M(t-
mtaa)L2] species, the arrangement of the two L ligands
can be either cis or trans, depending on the degree that
the metal is out of the N4 plane, and is a direct
consequence of the dn configuration.2d In the case of
metals with a low-spin d6 configuration, the arrange-
(16) Eaton, G. R.; Eaton, S. S. J . Am. Chem. Soc. 1975, 97, 235.

Ruthenium-Carbene Functionality
Organometallics, Vol. 18, No. 3, 1999 365
Ta ble 2. Selected Geom etr ica l P a r a m eter s for 5 a n d 6: Bon d Len gth s a n d Meta l Ou t-of-P la n e Dista n ces
(d )a Ar e in An gstr om s; Bon d a n d Dih ed r a l (r a n d â)bAn gles in Degr ees
5
6
5
6
Ru-C(23)
Ru-C(28)
Ru-N(1)
Ru-N(2)
Ru-N(3)
Ru-N(4)
N(1)-C(21)
N(1)-C(1)
N(2)-C(7)
N(2)-C(6)
1.980(4)
2.013(4)
2.032(3)
2.035(3)
2.040(3)
2.038(4)
1.334(5)
1.411(5)
1.333(5)
1.414(5)
1.874(8)
N(3)-C(10)
N(3)-C(12)
N(4)-C(18)
N(4)-C(17)
N(5)-C(23)
N(5)-C(24)
N(6)-C(28)
N(6)-C(29)
C(23)-C(24)
C(23)-C(30)
1.324(5)
1.409(5)
1.338(5)
1.394(5)
1.155(5)
1.453(5)
1.149(5)
1.460(5)
1.331(9)
1.432(9)
1.356(10)
1.426(9)
2.044(6)
2.024(6)
2.034(6)
2.028(7)
1.333(9)
1.417(9)
1.351(10)
1.426(9)
1.489(10)
1.495(10)
C(23)-Ru-C(28)
C(23)-Ru-N(1)
C(28)-Ru-N(1)
C(23)-Ru-N(2)
C(28)-Ru-N(2)
N(1)-Ru-N(2)
C(23)-Ru-N(3)
C(28)-Ru-N(3)
N(1)-Ru-N(3)
N(2)-Ru-N(3)
C(23)-Ru-N(4)
C(28)-Ru-N(4)
N(1)-Ru-N(4)
N(2)-Ru-N(4)
N(3)-Ru-N(4)
C(21)-N(1)-C(1)
C(21)-N(1)-Ru
173.9(2)
C(1)-N(1)-Ru
112.2(2)
128.8(3)
118.9(3)
112.3(3)
128.8(4)
119.1(3)
112.1(3)
129.1(4)
118.3(3)
112.4(3)
168.0(4)
168.5(4)
171.9(3)
172.8(4)
110.4(5)
127.1(6)
121.2(5)
111.6(5)
126.7(6)
121.7(5)
110.9(5)
126.6(6)
121.4(5)
112.0(5)
92.94(14)
88.57(14)
94.79(14)
91.31(14)
81.83(13)
86.84(14)
91.58(14)
179.35(14)
98.80(14)
88.35(14)
85.55(14)
98.57(14)
176.81(13)
80.81(14)
128.9(3)
98.1(3)
C(7)-N(2)-C(6)
C(7)-N(2)-Ru
102.4(3)
C(6)-N(2)-Ru
C(10)-N(3)-C(12)
C(10)-N(3)-Ru
C(12)-N(3)-Ru
C(18)-N(4)-C(17)
C(18)-N(4)-Ru
C(17)-N(4)-Ru
C(23)-N(5)-C(24)
C(28)-N(6)-C(29)
N(5)-C(23)-Ru
N(6)-C(28)-Ru
C(24)-C(23)-Ru
C(30)-C(23)-Ru
80.2(3)
97.4(3)
164.5(2)
96.7(3)
101.6(3)
96.4(3)
156.0(2)
80.2(3)
126.4(6)
121.9(5)
122.5(5)
122.3(5)
118.8(3)
R1
â1
d
18.0(1)
12.3(2)
0.026(2)
18.1(3)
25.8(5)
0.347(3)
R2
â2
22.2(1)
19.7(1)
19.0(3)
29.9(3)
a
b
Distance of Ru atom from N4 donor plane. Dihedral angles between N4 donor plane and C1‚‚‚C6 benzenoid ring ) R1; between N4
and C12‚‚‚C17 benzenoid ring ) R2; between N4 and C7‚‚‚C11 carbons of pentanediiminate ring ) â1; between N4 and C18‚‚‚C22
pentanediiminate ring ) â2.
Sch em e 2
mally in isonitrile derivatives (Table 2). Larger distor-
tions were observed for the porphyrin complex and are
explained by crystal packing influences.17
(b) Ru th en iu m -tm ta a -Ca r ben e Com p lexes. The
synthesis of ruthenium-carbene functionalities bonded
to a macrocyclic ligand is displayed in Scheme 2. The
carbene derivatives 6-8 have been obtained by reacting
a THF suspension of 1 with the corresponding diazoal-
kane, preferably at -20/-30 °C. The reaction produces
crystalline solids in good yield. These species were easily
characterized by their low-field 13C signals, indicative
of a coordinated carbene: 291.8 ppm for 6 and 279.2
ppm for 8. Although the corresponding signal was not
F igu r e 2. ORTEP drawing (thermal ellipsoid 50% prob-
ability) of complex 6.
electronic excited states, which results in a large
paramagnetic contribution to the chemical shift.18 The
1
tmtaa ligand has the usual H NMR spectrum with a
singlet for the meso-protons and the methyl groups.
The structure of a ruthenium-carbene functionality,
complex 6 containing THF of crystallization, is displayed
in Figure 2, with selected bond distances and angles in
Table 2. The coordination environment of ruthenium is
a distorted tetragonal pyramid, unlike that in carbene-
Fe,19 carbene-Os,20 and carbene-Rh21 porphyrins, where
1
seen for complex 7, the H NMR did show a character-
istic low-field signal centered at 17.1 ppm for the
carbene proton. This deshielding of the carbene signal
was explained by invoking the presence of low-energy
(18) Crabtree, R. H. The Organometallic Chemistry of the Transition
Metals, 2nd ed.; Wiley: New York, 1994; Chapter 11.
(17) J ameson, J . B.; Ibers, J . A. Inorg. Chem. 1979, 18, 1200.

366 Organometallics, Vol. 18, No. 3, 1999
Klose et al.
Sch em e 3
Sch em e 4
products. Alkylation of this material with MeI does not
lead to the desired carbene, but partially to the corre-
sponding methoxy-functionalized isonitrile complex.
This synthetic approach was unsuccessful due to the
very low electrophilicity of the isocyanide carbon bonded
to the unexpectedly electron-rich ruthenium. Theoretical
calculations (vide infra), in fact, suggest an abnormal
negative charge on the metal, as expected for a d8 rather
than for a d6 configuration.
(c) Liga n d -In d u ced La biliza tion of th e Ru -
Ca r ben e F u n ction a lity. The carbene complexes 6-8
are particularly thermally stable, but they undergo easy
labilization by a trans-incoming ligand under the condi-
tion that it has an appropriate balance between σ-do-
nating and π-accepting binding properties. As a matter
of fact, they are particularly sensitive to ligands such
as CO, RNC, and PR3, but not to pyridine. When
solutions of 6-8 are reacted with carbon monoxide (1
atm) at room temperature and in THF solution, three
different reaction pathways are observed, depending on
the substituents on the carbene carbon.
In the case of 6, complex 10 was isolated (see Scheme
4), which corresponds to the simple coordination of
carbon monoxide trans to the diphenylcarbene frag-
ment. No color changes were observed in the reaction
of 6 with CO, but a typical IR band at 1906 cm-1 and
the 13C NMR peak at 270.9 ppm confirm the coordina-
tion of CO. Surprisingly, the chemical shift of the
carbene carbon signal is virtually unaffected. In the case
of 10, the very low CO stretching frequency is indicative
of an electron-rich [Ru(tmtaa)] fragment and indirectly
supports (vide infra) the terminology we use for such
Ru derivatives, namely, that of a carbene, instead of an
alkylidene.
In the case of 7 and 8, the reaction proceeds behind
the simple coordination. The trans carbon monoxide
labilizes the carbene, causing its migration to the
macrocycle with a quite different synthetic result,
depending on the substituents R and R′. In the case of
R ) Ph, R′ ) COOMe (complex 8, Scheme 5) we can
suppose the labilized carbene carbon bridging the metal
and the meso-carbon. A bridging bonding mode of the
carbene carbon, like that observed between iron and one
of the nitrogens of the porphyrin,27 is, however, pre-
vented by the distance between the metal and the meso-
the metal is always hexacoordinate. The metal is
displaced by 0.374(3) Å from the N4 average plane
toward the carbene carbon. The Ru-C23 vector is
perpendicular to the N4 core. The carbene C23,C24,C30
plane is almost parallel to the N1-N3 vector, the
torsional angles C30,C23,Ru,N3 and C24,C23,Ru,N2
being -6.6(6)° and -91.0(6)°, respectively. The RudC
bond distance [1.874(8) Å], which does not have any
reference in Ru-porphyrin or macrocyclic chemistry, is
rather close to those found in Ru-phosphine deriva-
tives.7,22 The question of whether the oxidation state of
Ru in 6 is II or IV can be reasonably answered by
considering the Ru distance from the N4 plane.23 The
value found in the present case [0.347(3) Å)] is that
expected for a low-spin d6, compared with 0.216(5) Å in
[Ru(tmtaa)(CO)(thf)], 3.24 A much longer distance would
be expected for a d4 configuration. The tmtaa ligand has
the usual saddle shape conformation.2
Two other synthetic approaches have been tried in
order to get the Ru-carbene functionality bonded to a
macrocycle. The first one involves reacting 1 with an
electron-rich alkene such as bis(1,3-diphenylimidazo-
lidinylidene-2). Attempts to initiate the C-C scission
in refluxing THF or toluene were unsuccessful, as
strictly no reaction occurred. In contrast, it has been
reported that [RuCl2(PPh3)3] reacts with the same
electron-rich alkene under similar conditions to form the
surprising tetracarbene trans-dichlorotetrakis (1,3-
diphenylimidazolidinylidene-2) ruthenium(II).25 The sec-
ond strategy is based on the reaction of coordinated
isonitriles with nucleophiles and more specifically on
the work of Hahn and co-workers.26 The formation of
the isonitrile complex 9 occurs easily (Scheme 3). The
characteristic IR(CN) band at 1997 cm-1 and the 13C
NMR at 208.8 ppm are typical of a coordinated isoni-
trile. The hydrolysis of the Si-O bond was done in
MeOH and resulted in a mixture of poorly defined
(19) Mansuy, D.; Lange, M.; Chottard, J . C.; Bartoli, J . F.; Chevrier,
B.; Weiss, R.; Angew. Chem. 1978, 90, 828.
(20) Djukic, J .-P.; Smith, D. A.; Young, V. G., J r.; Woo, L. K.
Organometallics 1994, 13, 3020.
(21) Boschi, T.; Licoccia, S.; Paolesse, R.; Tagliatesta, P. Organo-
metallics 1989, 8, 330.
(22) (a) Schwab, P.; Grubbs, R. H.; Ziller, J . W. J . Am. Chem. Soc.
1996, 118, 100. (b) Esteruelas, M. A.; Lahoz, F. J .; On˜ate, E.; Oro, L.
A.; Zeier, B. Organometallics 1994, 13, 4258.
(23) A correlation in tmtaa complexes has been established between
the out-of-plane distance of the metal and its dn configuration: see ref
2d.
(27) (a) Brothers, P. J .; Collman, J . P. Acc. Chem. Res. 1986, 19,
209. (b) Mansuy, D. Pure Appl. Chem. 1987, 59, 759. (c) Artaud, I.;
Gregoire, N.; Battioni, J .-P.; Dupre, D.; Mansuy, D. J . Am. Chem. Soc.
1988, 110, 8714. (d) Artaud, I.; Gregoire, N.; Leduc, P.; Mansuy, D. J .
Am. Chem. Soc. 1990, 112, 6899. (e) Mansuy, D.; Mahy, J . P. In
Metalloporphyrins Catalyzed Oxidations; Montanari, F., Casella, L.,
Eds.; Kluwer: Dordrecht, The Netherlands, 1994; pp 175-206. (f)
Latos-Grazynski, L.; Cheng, R.-J .; La Mar, G. N.; Balch, A. L. J . Am.
Chem. Soc. 1981, 103, 4270. (g) Balch, A. L.; Cheng, R.-J .; La Mar, G.
N.; Latos-Grazynski, L. Inorg. Chem. 1985, 24, 2651.
(24) Unpublished results.
(25) Hitchcock, P. B.; Lappert, M. F.; Pye, P. L. J . Chem. Soc., Dalton
Trans. 1978, 826. Hitchcock, P. B.; Lappert, M. F.; Pye, P. L. J . Chem.
Soc., Chem. Commun. 1976, 644.
(26) Hahn, F. E.; Tamm, M. Organometallics 1995, 14, 2597. Hahn,
F. E.; Tamm, M.; Lu¨gger, T. Angew. Chem, Int. Ed. Engl. 1994, 33,
1356. Hahn, F. E.; Tamm, M. J . Organomet. Chem. 1993, 456, C11.
Hahn, F. E. Angew. Chem, Int. Ed. Engl. 1993, 32, 650.

Ruthenium-Carbene Functionality
Organometallics, Vol. 18, No. 3, 1999 367
C9,C10,N3 with C9 displaced 0.315(4) Å out of the N2,
C7,C10,N3 plane. As a consequence, C7-N2 [1.270(5)
Å] and C10-N3 [1.278(5) Å] become imino groups and
the meso-alkylated tmtaa now functions as a monoan-
ionic ligand. The bonding sequence shown for the bridge
across the sp3 C9 and Ru in Scheme 5 is supported by
(i) the C23-C25 [1.390(5) Å] double-bond character; (ii)
the planarity of the bridge, the C23-C25-C26-C27
having a torsional angle of -7.8(6)°; and (iii) some
lengthening of the C23-O1 [1.260(4) Å] bond, which is
in agreement with a charge delocalization over the O1-
C23-C25 fragment functioning as a monoanionic oxoal-
lyl moiety. The modified tmtaa in 11 maintains the
saddle shape conformation with the two phenyl groups
tilted up in the same direction as the Ru-CO vector.
This is always the case when one of the axial ligands is
multiple bonded to the metal [see complex 6 and [Ru-
(tmtaa)(CO)(thf)], 3]. The Ru-C32 [1.793(5) Å] bond
distance is close to that in 3 [1.761(6) Å] and signifi-
cantly shorter than that found in other octahedral Ru-
(II) complexes having an oxygen donor ligand trans to
CO.29
F igu r e 3. ORTEP drawing (thermal ellipsoid 50% prob-
ability) of complex 11.
The reaction pathway of 7 upon labilization by carbon
monoxide (see Scheme 6) involves, in its preliminary
stage, the migration of the carbene carbon to a CdC
bond of the diiminato ring. This step is followed by a
hydrogen shift to form the seven-membered metallacycle
(see complex 12), within the metal-macrocycle moiety.
The resulting novel macrocycle, which becomes confor-
mationally more flexible, rearranges around the metal
and leaves two cis coordination sites available for carbon
Sch em e 5
1
monoxide. The H NMR of complex 12 shows a signifi-
cant loss of symmetry. The methyl groups are no longer
equivalent and show four signals. Apart from the
aromatic region, one singlet and two doublets, each
integrating as one proton, are observed. The DEPT and
proton-carbon correlation experiments clearly show
that a CH2 unit was formed, which corresponds to the
two previous doublets. Supporting evidence is given by
the IR, which shows two characteristic CO bands at
2016 and 1948 cm-1, and by the two 13C NMR signals
at 199.8 and 197.5 ppm. It should be mentioned, at this
stage, that although in a different context, migration
of alkyl groups from the metal to the imino carbons of
the macrocycle ligand tmtaa has been observed in the
[Zr(tmtaa)]2f and [Nb(tmtaa)] organometallic chemis-
try.30 The proposed bonding scheme for 12 is confirmed
by the structural parameters (Table 4) related to the
structure of 12 shown in Figure 4. The new macrocyclic
ligand contains two five-membered, one six-membered,
and one seven-membered ring. In the last mentioned
ring, the nitrogen donor atom N1 becomes an imido
group with the related sp3 geometry and a short Ru-
N1 distance [2.060(5) Å], while the neutral imino sp2
nitrogen N4 binds Ru with a long distance [Ru-N4,
2.223(5) Å]. The two cis-arranged CO experience a
different trans influence by N2 and N4; thus, the longer
Ru-C30 bond [1.882(6) Å] is trans to an amino and the
shorter Ru-C31 [1.833(6) Å] to an imido group.
carbon. Therefore, the attack at the meso-carbon by the
carbene is followed by a rearrangement of the carbene
fragment to a geometrically more appropriate bridging
unit, such as the one in complex 11. A structural
analogue can be found in cobalt(III)-tmtaa chemistry,
where a vinyl group bridges the metal and the macro-
cyclic ligand.28 Complex 11 shows a partial loss of
symmetry in its 1H NMR spectrum. Two important
features are observed. First, there are only two signals
for the CH3 groups integrating for 6H each, implying a
mirror plane in the molecule. Second, there are two
different CH peaks, which also imply a new chemical
environment. A single CO band was detected by IR
(1905 cm-1) and 13C NMR (211.9 ppm) spectra. The
structure of 11 is shown in Figure 3, and its selected
parameters are given in Table 3. The transfer of the
carbene carbon to C9 removes the aromaticity and the
planarity of the six-membered metallacycle Ru,N2,C7,
The reaction of 7 and 8 with ButNC parallels the
reaction with carbon monoxide, and due to the close
(29) Alessio, E.; Milani, B.; Bolle, M.; Mestroni, G.; Faleschini, P.;
Todone, F.; Geremia, S.; Calligaris, M. Inorg. Chem. 1995, 34, 4722,
and references therein.
(28) Weiss, M. C.; Goedken, V. L. J . Am. Chem. Soc. 1976, 98, 3389.
Weiss, M. C.; Gordon, G. C., Goedken, V. L. J . Am. Chem. Soc. 1979,
101, 857.
(30) Unpublished results.

368 Organometallics, Vol. 18, No. 3, 1999
Klose et al.
Ta ble 3. Selected Geom etr ica l P a r a m eter s for 11: Bon d Len gth s a n d Meta l Ou t-of-P la n e Dista n ces (d )a Ar e
in An gstr om s; Bon d a n d Dih ed r a l (r a n d â)b An gles in Degr ees
Ru-C(32)
Ru-N(1)
Ru-N(2)
Ru-N(3)
Ru-N(4)
Ru-O(1)
O(1)-C(23)
O(2)-C(23)
1.793(5)
2.011(3)
2.024(3)
2.006(3)
2.027(3)
2.134(3)
1.260(4)
1.368(4)
O(3)-C(32)
N(1)-C(21)
N(1)-C(1)
N(2)-C(7)
N(2)-C(6)
N(3)-C(10)
N(3)-C(12)
1.165(5)
1.318(5)
1.417(5)
1.270(5)
1.428(5)
1.278(5)
1.429(5)
N(4)-C(18)
N(4)-C(17)
C(7)-C(9)
C(9)-C(10)
C(9)-C(25)
C(23)-C(25)
C(25)-C(26)
1.340(5)
1.408(5)
1.518(5)
1.529(6)
1.538(5)
1.387(5)
1.453(5)
C(32)-Ru-N(3)
C(32)-Ru-N(1)
N(3)-Ru-N(1)
C(32)-Ru-N(2)
N(3)-Ru-N(2)
N(1)-Ru-N(2)
C(32)-Ru-N(4)
N(3)-Ru-N(4)
N(1)-Ru-N(4)
N(2)-Ru-N(4)
C(32)-Ru-O(1)
95.6(2)
95.3(2)
N(3)-Ru-O(1)
N(1)-Ru-O(1)
N(2)-Ru-O(1)
N(4)-Ru-O(1)
C(23)-O(1)-Ru
C(21)-N(1)-C(1)
C(21)-N(1)-Ru
C(1)-N(1)-Ru
C(7)-N(2)-C(6)
C(7)-N(2)-Ru
84.51(12)
84.58(12)
83.22(11)
86.56(11)
137.2(2)
128.1(4)
119.3(3)
112.1(2)
125.7(4)
120.1(3)
C(6)-N(2)-Ru
111.9(2)
127.1(3)
118.8(3)
111.8(2)
128.2(4)
119.5(3)
112.1(3)
127.4(3)
105.7(3)
105.6(3)
C(10)-N(3)-C(12)
C(10)-N(3)-Ru
C(12)-N(3)-Ru
C(18)-N(4)-C(17)
C(18)-N(4)-Ru
C(17)-N(4)-Ru
C(7)-C(9)-C(10)
C(7)-C(9)-C(25)
C(10)-C(9)-C(25)
169.08(13)
96.0(2)
98.94(13)
80.36(13)
94.2(2)
80.32(13)
98.40(13)
169.77(13)
179.2(2)
R1
â2
d
18.4(2)
24.4(3)
0.186(2)
R2
18.8(2)
â1
27.1(2)
a
b
Distance of Ru atom from N4 donor plane. Dihedral angles between N4 donor plane and C1‚‚‚C6 benzenoid ring ) R1; between N4
and C12‚‚‚C17 benzenoid ring ) R2; between N4 and C7, C8, C10, C11 ) â1; between N4 and C18‚‚‚C22 carbons of pentanediiminate ring
) â2.
Sch em e 6
electron density of the metal in 6 and the powerful
σ-donor ability of ButNC. We should mention at this
stage that the balance between the σ-donor and π-ac-
ceptor properties of the axial ligand plays a major role
in the activation of the carbene functionality, determin-
ing its labilization pathway. This can follow a free-
radical type mechanism (Scheme 5) or a more carbene-
like pathway (Scheme 6) (vide infra).
With the general aim of understanding the relevance
of the σ-donor and π-acceptor properties of the axial
ligand, we moved from carbon monoxide and isonitrile
to pyridine and phosphines. The former choice was for
a ligand having both a poor π-acceptor and not very
strong σ-donating properties. Complexes 6-8 were
converted into hexacoordinated ruthenium carbene
derivatives 15-17 (Scheme 8) in the reaction with
pyridine. The coordination of the sixth ligand trans to
the carbene functionality did not cause any labilization
of the carbene functionality, as it did in the case of CO
and RNC. The presence of the pyridine ligand in
complexes 15-17 was revealed by some significant shift
in the 13C resonance of the carbene carbon (see Experi-
mental Section).
Phosphines are an excellent class of ligands for
helping define the limits of the carbene labilization,
being excellent σ-donors, good trans labilizing agents,
and poor π-acceptors. Fine-tuning of the electronic
properties can be achieved by the use, eventually, of
different substituents at phosphorus. Therefore we
reacted carbene complexes 6-8 with trimethylphos-
phine, which amounts to a decrease in the π-acidity and
increase in the σ-basicity. Strictly no reaction occurred
with the stable diphenylcarbene derivative 6, in contrast
with carbenes 7 and 8 (see Scheme 9). When complex 7
was reacted in toluene at -30 °C with 1 or 2 equiv of
the corresponding phosphine, the bis(phosphine) com-
pounds 18 formed as a green crystalline material, as
confirmed by NMR spectroscopy and elemental analysis
(Scheme 9). A GC analysis of the mother liquor showed
relationship between CO and RNC in terms of σ and π
properties, we suppose that the reactions follow the
same pathway displayed in Schemes 5 and 6. When
complex 7 was reacted with 2 equiv of ButNC (see
Scheme 7), complex 13 was obtained as a crystalline
green material. NMR evidence implies that its structure
is similar to complex 12 (Scheme 7). Similarly, four
signals were observed for the methyl groups of the
tmtaa due to the loss of symmetry in the ligand, further
supported by two But peaks at 0.96 and 0.82 ppm. The
DEPT and the 1H-13C correlation experiments con-
firmed the presence of a CH2 group, which appeared as
two doublets in the 1H NMR. We note that they are
particularly more deshielded than in complex 12. When
8 was reacted with ButNC in toluene, complex 14 slowly
1
formed (Scheme 7). The H NMR spectrum is similar
to complex 11 with an additional peak corresponding
to the But group. Only slight variations in the chemical
shift were observed. An IR band centered at 1934 cm-1
and the 13C NMR signals at 190.7 ppm characterized
the single coordinated isonitrile. Complex 6 did not bind
with ButNC, due to the incompatibility between the high

Ruthenium-Carbene Functionality
Organometallics, Vol. 18, No. 3, 1999 369
Ta ble 4. Selected Bon d Len gth s (Å) a n d An gles (d eg) for 12
Ru-C(30)
Ru-C(31)
Ru-N(1)
Ru-N(2)
Ru-N(3)
Ru-N(4)
1.882(6)
1.833(6)
2.060(5)
2.102(4)
2.078(5)
2.223(5)
N(1)-C(1)
N(1)-C(28)
N(2)-C(7)
N(2)-C(6)
N(3)-C(10)
N(3)-C(12)
1.381(7)
1.420(7)
1.337(7)
1.427(7)
1.338(7)
1.431(7)
N(4)-C(18)
N(4)-C(17)
C(18)-C(20)
C(20)-C(21)
C(21)-C(28)
1.289(7)
1.441(7)
1.502(9)
1.537(8)
1.344(8)
C(31)-Ru-C(30)
C(31)-Ru-N(1)
C(30)-Ru-N(1)
C(31)-Ru-N(3)
C(30)-Ru-N(3)
N(1)-Ru-N(3)
C(31)-Ru-N(2)
C(30)-Ru-N(2)
N(1)-Ru-N(2)
N(3)-Ru-N(2)
91.2(2)
92.0(2)
96.5(2)
99.3(2)
96.3(2)
162.7(2)
83.4(2)
173.6(2)
80.3(2)
87.9(2)
C(31)-Ru-N(4)
C(30)-Ru-N(4)
N(1)-Ru-N(4)
N(3)-Ru-N(4)
N(2)-Ru-N(4)
C(1)-N(1)-C(28)
C(1)-N(1)-Ru
C(28)-N(1)-Ru
C(7)-N(2)-C(6)
C(7)-N(2)-Ru
173.4(2)
86.7(2)
94.4(2)
74.8(2)
99.0(2)
118.9(5)
112.8(4)
115.0(4)
124.7(5)
118.9(4)
C(6)-N(2)-Ru
112.4(3)
123.0(5)
124.4(4)
110.4(3)
122.4(5)
131.7(4)
105.7(3)
177.3(6)
178.6(5)
C(10)-N(3)-C(12)
C(10)-N(3)-Ru
C(12)-N(3)-Ru
C(18)-N(4)-C(17)
C(18)-N(4)-Ru
C(17)-N(4)-Ru
O(1)-C(30)-Ru
O(2)-C(31)-Ru
Sch em e 8
Sch em e 9
F igu r e 4. ORTEP drawing (thermal ellipsoid 50% prob-
ability) of complex 12.
Sch em e 7
31P NMR spectra show singlets at 1.11 and 0.55 ppm,
respectively, which corresponds to coordinated PMe3.
The 31P NMR signal of the free phosphine is at -62.0
ppm.31 These data nicely support a structure similar to
that observed for complexes 11 and 14. The PMe3
ligand, based on the results in Scheme 9, considerably
affects the labilization pathway of the Ru-carbene
functionality. First of all the absence of any reaction
with 6 is in agreement with the poor π-acceptor proper-
ties and the strong σ-donor ability of the ligand, as we
mentioned for the different reactivity of 6 toward CO
and RNC. The formation of 18 and stilbenes from 7
would be understandable admitting that the labilization
caused by a strong σ-donor like PMe3 generates a free
carbene. The formation of 19 from the reaction of 8 with
the presence of cis- and trans-stilbene, 86% and 14%,
respectively. The reaction of 8 with PMe3 in toluene led
to 19. Good analytical data were obtained for the
recrystallized product. The increased complexity of the
1H NMR spectrum implies a loss of symmetry similar
(31) Verkade, J . G.; Quin, L. D. Phosphorus-31 NMR Spectroscopy
in Stereochemical Analysis; VCH: Berlin, 1987; Vol 8.
1
to that observed for complexes 11 and 14. The H and

370 Organometallics, Vol. 18, No. 3, 1999
Klose et al.
Ta ble 5. Ma in P a r a m eter s Descr ibin g th e
In ter a ction betw een th e [Ru (tm ta a )] Meta l
F r a gm en t a n d th e CRR′ Moiety (See Text)
R, R′
parameter
H, H
Ph, H
Ph, Ph Ph, COOMe
ꢀ(b2)
P(b2)
-11.40 -10.79 -11.03
-11.52
1.10
0.95
1.54
0.76
1.00
0.87
0.87
∆[HOMO-π*(M-C)]
Q(Ru)
Q(carbene-C)
Q(meso-C)
Q(CRR′)
0.43
+0.72
-0.26
-0.30
-0.29
+0.46
-0.21
-0.30
-0.14
+0.36
-0.13
-0.30
-0.03
+0.58
-0.21
-0.30
-0.33
a1(sp2 hybrid) and the π-acceptor b2(py). The interaction
between the [Ru(tmtaa)] fragment and the CH2 unit is
illustrated by the molecular orbital diagram for the [Ru-
(tmtaa)(CH2)] complex in the fourth column of Figure
5. In the [Ru(tmtaa)CPh2)] complex, the only one whose
X-ray structure is available, the orientation of the
carbene unit is such that the CPh2 plane forms an angle
of about 39° with the xz symmetry plane bisecting the
diiminato rings. However, to keep the C2v symmetry of
the metal fragment and simplify the analysis of the
results, we considered an orientation with the CH2 plane
lying in the xz symmetry plane. Figure 5 shows a strong
F igu r e 5. Building of the molecular orbitals of [Ru(tmtaa)]
and orbital interaction diagram for [Ru(tmtaa)(CH2)].
PMe3 (Scheme 9) once again suggests, however, a free-
radical pathway. This may be the consequence of the
presence of the COOMe substituent at the carbene
carbon having a significant π-acceptor contribution.
Exten d ed Hu1 ck el An a lysis on th e [Ru (tm ta a )]
Com p lexes. Extended Hu¨ckel calculations32,33 were
performed to elucidate the nature of the bonding in some
of the complexes considered and to understand the
labilization of the Ru-carbene functionality by a trans
incoming ligand.
2
interaction between the 1a1(dz ) and the σ-donor 1a1 of
CH2 and between the 1b2(dyz) and the π-acceptor b2. In
principle the π-acceptor orbital of CH2 could interact
with both the doubly occupied b2(dyz) and b1(dxz) metal
orbitals, leading to different orientations of the carbene
moiety with the CH2 unit lying in the xz and yz planes,
respectively. The latter orientation has been calculated
as being ca. 0.3 eV more stable, probably due to the more
favorable interaction of the carbene π-acceptor orbital
with the higher-lying 1b1(dxz) donor orbital. The appar-
ent disagreement with the experimental X-ray structure
can be rationalized by noting that the electronically
most favorable orientation of the carbene moiety along
the yz plane would lead to strong steric repulsion
between the two bent benzo groups and the carbene
phenyl substituents. The observed orientation is there-
fore a compromise between electronic factors favoring
the orientation of the CPh2 in the yz plane and steric
repulsion favoring the orientation of the carbene in the
xz plane. A calculation performed on the real CPh2
carbene confirmed that the orientation of the carbene
plane in the yz plane would lead to a strong steric
destabilization.
The molecular orbitals of the [Ru(tmtaa)] fragment
are built in a step-by-step approach. We first considered
the planar (tmtaa)2- ligand of D2h symmetry, which was
then deformed so as to reproduce the geometry of the
(tmtaa) skeleton in the final complex.2f,34 The molecular
orbitals for the planar (tmtaa)2- ligand are reported in
the first column of Figure 5, while in the second one we
illustrate the effect of the bending up of the two benzo
groups (18.5°) and the bending down of the two allyl
groups (28.0°). We finally added Ru in the middle of the
(tmtaa) ring, and the resulting MO diagram is reported
in the third column of Figure 5. Upon coordination, the
d orbitals mix strongly with the ligand frontier orbitals
so that no pure d orbitals can be assigned. However five
MOs with large metal d characters can be identified.
2
These are the three highest occupied orbitals a1(dz ), b2-
Extended Hu¨ckel calculations have been performed
on all the synthesized [Ru(tmtaa)(CRR′)] complexes 6-8
with R ) R′ ) Ph; R ) Ph, R′ ) H; and R ) Ph, R′ )
COOMe, respectively. The molecular orbital diagrams
for these complexes is quite similar to that in Figure 5
for the CH2 carbene. However, the presence of different
substituents on the carbene unit affects the energy of
the π-acceptor orbital b2(py), thus changing some details
of the molecular orbital diagram. In Table 5 we report
the main parameter describing the interaction between
the metal fragment and the CRR′ group, notably (i) the
energy of the CRR′ π-acceptor orbital; (ii) its population
in the carbene complex; (iii) the energy gap between the
2
2
(dyz), b1(dxz) and the lowest unoccupied orbital a1(dx -y
)
lying in the N4 ligand plane. The a2(dxy) pointing more
closely toward the nitrogen atoms of tmtaa is pushed
high in energy. The second and third LUMOs cor-
respond closely to the two LUMOs of the (tmtaa)2-
distorted ligand, au and b3g.
We then considered the bonding between the CRR′
unit and the central metal in the [Ru(tmtaa)CRR′)]
carbene complexes, first using the simplest R ) R′ ) H
case, which enables us to simplify the discussion and
change the orientation of the carbene plane without
introducing steric effects. On the extreme right of Figure
5 we show the frontier orbitals of CH2, i.e., the σ-donor
2
2
HOMO (mainly a dx -y metal orbital in all cases) and
the low-lying orbital of antibonding dyz(Ru)-py(C) π(M-
C) character; (iv) the atomic charge on ruthenium,
carbene carbon, and diiminato meso-carbon atom; (v)
(32) Hoffmann, R.; Lipscomb, W. N. J . Chem. Phys. 1962, 36, 2179.
(33) Hoffmann, R. J . Chem. Phys. 1963, 39, 1397.
(34) Tatsumi, K.; Hoffmann, R. Inorg. Chem. 1981, 20, 3771.

Ruthenium-Carbene Functionality
Organometallics, Vol. 18, No. 3, 1999 371
2
strong destabilization of the dz orbital (interacting with
the carbon lone pair of CO) and a significant stabiliza-
tion of the two dxz, dyz orbitals (due to their interactions
with the empty π* orbitals of CO). Both effects lead to
a higher energy mismatch between these metal orbitals
and the interacting counterparts on the carbene unit
and thus to a labilization of the metal-carbene bonding.
Extended Hu¨ckel calculations have been performed on
complexes 6-8 coordinated by a trans Py, CO, and PMe3
ligand. We used the X-ray geometry of 6 (with plausible
values for the geometry of the H or COOMe carbene
substituent in 7 and 8) including the ligand at a suitable
distance from ruthenium with the free molecule geom-
etry. No significant variation of the parameters describ-
ing metal-carbene interaction is observed upon coor-
dination of a weak σ-donating ligand like pyridine and
is in agreement with the observed stability of 6-8 in
the presence of pyridine, leading only to the hexacoor-
dinated carbene species 15-17. A different situation is
observed for a strong π-acid (CO) or a strong σ-donating
(PMe3) ligand, for which a significant variation of these
parameters is observed (mainly a reduction of the pop-
ulation of the π-acceptor orbital of carbene and a de-
crease in the energy gap between the HOMO, essen-
F igu r e 6. Orbital interaction diagram for [Ru(tmtaa)(CO)-
(CH2)] showing the effect of CO coordination.
the electron donation from the metal fragment to the
CRR′ group.
2
2
tially a dx -y orbital, and the LUMO, of antibonding dyz-
(Ru)-py(C) character), showing a weakening of the
metal-carbene bond. Therefore a labilization of the Ru-
carbene functionality upon CO or PMe3 coordination is
expected for 6-8 and actually observed for 7 and 8.
For complex 7 this labilization probably leads to a
detachment of a :CRR′ carbene, which then inserts into
a C-C bond of the diiminato ring, leading to the seven-
membered metallacycle. Such a carbene-mediated mech-
anism is supported by the presence in the mother liquor
of the reaction of cis- and trans-stilbene between 7 and
PMe3. A different situation is found for 8 (R ) Ph, R′ )
COOMe), for which the low energy of the pπ CRR′ unit
leads to a small HOMO-LUMO gap, which is further
reduced by trans coordination by CO and PMe3 (less
than 0.3 eV). Therefore, upon trans coordination, 8 is
expected to generate a free radical at the carbene carbon
attacking the meso-position of the tmtaa ligand, then
rearranging to the bridging moiety in 11.
To explain why the carbene labilization is not ob-
served for 6, although plausible on purely electronic
grounds, we should mention that the calculations con-
cern only the first step of the Ru-carbene labilization,
i.e. the initial trans coordination of the incoming ligand,
and use the geometry of the unperturbed carbenes with
the metal displaced by 0.374 Å from the N4 average
plane toward the carbene carbon (see above). However,
the real labilization process proceeds behind the simple
coordination, passing probably through an inversion of
the out-of-plane of ruthenium from the carbene toward
the incoming ligand. This inversion is suggested for
example by the X-ray structure of 3,24 which shows an
out-of-plane of Ru toward the CO ligand. For complex
6, probably, the steric crowding of the phenyl susbtitu-
ents with the benzo groups of the tmtaa macrocyle does
not allow such an out-of-plane inversion toward the
coordinated ligand, thus preventing carbene labilization.
For all these complexes, the interaction between the
[Ru(tmtaa)] fragment and the CRR′ group is typical of
most of the known metal carbene species.35 In particular
frontier orbital criteria suggest a Fisher carbene nature
for this [Ru(tmtaa)(CRR′)] species rather than a Schrock
alkylidene, in accordance with the accepted terminology.
This is supported by (i) the low energy of the metal dπ
orbitals, lower than that of the π-acceptor b2 orbitals
(see Table 5); and (ii) the presence of a low-lying π*-
(M-C) LUMO of high carbon character (see Figure 5)
which gives a significant electrophilic character to the
carbene moiety, both effects being characteristic of
Fisher carbene systems. However, the carbene unit
shows a significant, although small, negative charge on
the carbon atom (-0.1/-0.3) and a significant popula-
tion on the π-acceptor b2, which are more typical of
Schrock alkylidenes. Therefore, 6-8 can be actually
described as intermediate between Fisher carbene and
Schrock alkylidene, without a definite electrophilic or
nucleophilic character of the carbene carbon, in agree-
ment with the observed poor reactivity toward both
nucleophilic and electrophilic species. We did not ob-
serve any reactivity with either lithium alkyls or B(C6-
F5)3. The small positive charge calculated on the ruthe-
nium atom (+0.3/+0.7) and the small electron donation
of the [Ru(tmtaa)] fragment to the CRR′ moiety upon
carbene formation (0.03/0.33) (see Table 5) lend evidence
to the attribution of a formal oxidation state of II and a
d6 configuration for ruthenium based on geometrical
evidence (see above).
We then considered the effect of the coordination of a
further ligand trans to the carbene unit. Figure 6 shows
the effect of the CO coordination (a ligand with both
σ-basic and π-acid properties) on the orbital levels of
the [Ru(tmtaa)] fragment and its consequences on the
interaction diagram between the resulting [Ru(tmtaa)-
(CO)] fragment and the CH2 unit. Figure 6 shows a
Con clu sion s
(35) Hoffmann, P. In Transition Metal Carbene Complexes; Do¨tz,
K. H., Fischer, H., Hoffmann, P., Kreissl, F. R., Schubert, U., Weiss,
K., Eds.; Verlag Chemie: Weinheim, 1983; p 113.
The macrocycle illustrated by the dibenzotetramethyl-
tetraaza[14]annulene seems to be particularly appropri-

372 Organometallics, Vol. 18, No. 3, 1999
Klose et al.
ate for supporting the ruthenium-carbene functionality.
The preorganized quasi-planar N4 chemical environ-
ment favors study of the reciprocal influence of the two
coordination sites trans to each other and, in particular,
facilitates investigation into which kind of ligand (i.e.
CO, PMe3, etc.) can induce the trans-labilization of the
carbene functionality and by which mechanism, namely,
free radical or carbene. The ligand-induced migration
of the carbene to the macrocyclic ligand has important
precedents in iron porphyrins of biological relevance.
The theoretical approach has been used to explain the
ligand-induced labilization of the carbene functionality.
Ack n ow led gm en t. We thank the “Fonds National
Suisse de la Recherche Scientifique” (Bern, Switzerland,
Grant No. 20-53336.98), Ciba Specialty Chemicals
(Basle, Switzerland), and Fondation Herbette (Univer-
sity of Lausanne, NR.) for financial support.
Su p p or tin g In for m a tion Ava ila ble: Tables giving crys-
tal data and structure refinement, atomic coordinates, bond
lengths and angles, anisotropic displacement parameters, and
hydrogen coordinates for 5, 6, 11, and 12 (17 pages). Ordering
information is given on any current masthead page.
OM980898P