Versatile routes to mono- and bis(alkynyl) manganese(II) and manganese (III) complexes via manganocenes

Organometallics 1999, 18, 1525-1541

1525

Ver sa tile Rou tes to Mon o- a n d Bis(a lk yn yl)

Ma n ga n ese(II) a n d Ma n ga n ese(III) Com p lexes via

Ma n ga n ocen es

Dieter Unseld, Vassily V. Krivykh,^†Katja Heinze, Ferdinand Wild, Georg Artus,

Helmut Schmalle, and Heinz Berke*

Institute of Inorganic Chemistry, University of Zu¨rich, Winterthurerstrasse 190,

8057 Zu¨rich, Switzerland

Received December 29, 1998

With the manganocenes (RC₅H₄)₂Mn (R ) H, Me) as starting materials, paramagnetic d⁵

half-sandwich complexes (RC₅H₄)Mn(dmpe)(CtCR′) (dmpe ) 1,2-bis(dimethylphosphino)-

ethane; R ) Me, R′ ) Ph, 1a ; R ) Me, R′ ) SiMe₃, 2a ; R ) H, R′ ) Ph, 1b; R ) H, R′ )

SiMe₃, 2b) have been prepared by the reaction with terminal or SnMe₃-substituted acetylenes

and dmpe. The derivatives 1a and 2a could be isolated, while 1b and 2b have been identified

in mixtures with the bis(dmpe)bis(acetylide)manganese species 3 (R′ ) Ph) and 4 (R′ )

SiMe₃). The latter compounds are obtained as the sole products, when the manganocenes

are reacted with dmpe and the corresponding acetylenes in a 1:2:2 ratio. 1a and 2a can be

reversibly oxidized to the corresponding cationic Mn(III) complexes [(MeC₅H₄)Mn(dmpe)-

(CtCR′)][BF₄] (R′ ) Ph, [1a ]⁺; R′ ) SiMe₃, [2b]⁺). Compounds 1a and 2a act as scavengers

of H^•radicals in the 1:1:1 reaction mixtures or in the presence of n-Bu₃SnH or (C₅Me₅)Mo-

(CO)₃H, forming the vinylidene species (MeC₅H₄)Mn(dmpe)(dCdC(H)R′) (R′ ) Ph, 5; R′ )

SiMe₃, 6). In the absence of a special H^•donor, 1a slowly dimerizes to give the binuclear

complex 7. A similar process occurs with [1a ]⁺to form the bis(carbyne) complex 8. 8 can be

reduced to 7 by a reaction with 2 equiv of (MeC₅H₄)₂Co, and in turn 7 can be oxidized to 8

with 2 equiv of a ferrocenium salt. Equal amounts of 7 and 8 comproportionate to afford the

mixed-valence complex [7]⁺. If applicable, the new compounds have been characterized by

spectroscopic (NMR, EPR, near-IR) and electrochemical measurements, as well as X-ray

diffraction studies (2a , 5, 7, and 8) and DFT calculations.

In tr od u ction

all metallocenes of the 3d transition-metal series.⁵They

are pyrophoric, hydrolyze instantaneously in contact

with water and acids,^1bundergo facile ring exchange

reactions characteristic of ionic cyclopentadienide com-

pounds,⁷and allow substitution of one cyclopentadienyl

ligand by three two-electron donors, e.g. L ) CO⁸or L

) P(OR)₃.⁹The mechanism of the last reaction is

presumably more complicated than a simple one-step

replacement of a cyclopentadienyl group, as redox

processes with L as a reducing agent are sometimes

involved. The analogous reaction with L ) PMe₃does

not proceed at all;⁹instead, the tertiary phosphine

adducts (R′C₅H₄)₂Mn(PR₃) (R′ ) H, Me; R₃) Me₃, Et₃,

Me₂Ph, MePh₂) are formed.¹⁰The chelating bis(phos-

phine) Me₂PCH₂CH₂PMe₂(1,2-bis(dimethylphosphino)-

ethane, dmpe) even gives rise to adducts with coordi-

nation of both phosphorus atoms.¹⁰The 1:1 adducts with

the more electronegative donors 3,5-dichloropyridine¹¹

and tetrahydrofuran¹²have “tilted” planar cyclopenta-

The first representatives of the manganocene family

(C₅H₅)₂Mn and (MeC₅H₄)₂Mn have been known for

around 40 years.¹Their electronic properties, especially

the high-spin/low-spin crossover, have attracted much

attention and have been studied extensively by photo-

electron²and EPR^3,4spectroscopy, by magnetic meas-

urements in solution,³by electron diffraction,⁵and by

NMR spectroscopy.^3,6The manganocenes have the long-

est M-C distances and exhibit the highest reactivity of

^†Present address: Nesmeyanov Institute of Organoelement Com-

pounds, Vavilov Street 28, V-334, Moscow, Russia 117813.

(1) (a) Fischer, E. O.; Leiphinger, H. Z. Naturforsch. 1955, B10, 353.

(b) Wilkinson, G.; Cotton, F. A.; Birmingham, J . M. J . Inorg. Nucl.

Chem. 1956, 2, 95.

(2) (a) Rabalais, J . W.; Werme, L. O.; Bergman, K. L.; Karlsson, L.;

Hussain, M.; Siegbann, K. J . Chem. Phys. 1972, 57, 1185. (b) Evans,

S.; Green, M. L. H.; J ewitt, B.; King, G. H.; Orchard, A. F. J . Chem.

Soc., Faraday Trans. 1974, 2, 356. (c) Cauletti, C.; Green, J . C.; Kelly,

M. R.; Powell, P.; van Tilborg, J .; Robbins, J .; Smart, J . J . Electron

Spectrosc. Relat. Phenom. 1980, 19, 327.

(3) Switzer, M. E.; Wang, R.; Rettig, M. F.; Maki, A. H. J . Am. Chem.

Soc. 1974, 96, 7669.

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1974, 96, 7833. (b) Ammeter, J . H. J . Magn. Reson. 1978, 30, 299.

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1978, 149, 219.

(6) (a) Hebendanz, N.; Ko¨hler, F. H.; Mu¨ller, G.; Riede, J . J . Am.

Chem. Soc. 1986, 108, 3281. (b) Cozak, D.; Gouven, F.; Demers, J . Can.

J . Chem. 1987, 6, 1912. (c) Ko¨hler, F. H.; Schlesinger, B. Inorg. Chem.

1992, 31, 2853.

(7) Switzer, M. E.; Rettig, M. F. J . Chem. Soc., Chem. Commun.

1972, 687.

(8) Fischer, E. O.; J ira, R. Z. Naturforsch. 1954, B9, 618.

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M.; Hursthouse, M. B. J . Am. Chem. Soc. 1984, 106, 2033.

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105, 6510.

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1988, 110, 173.

Publication on Web 03/25/1999

1526 Organometallics, Vol. 18, No. 8, 1999

Sch em e 1. Syn th esis of 1a , 1b, 2a , 2b, 3, 4, [1a ]⁺, a n d [2a ]⁺

Unseld et al.

dienyl rings in the solid state. In contrast to the dmpe

derivatives the tmeda (tetramethylethylendiamine) ad-

duct contains an η¹-Cp ring.¹³Neither the electronic

nature nor the chemical properties of these unusual,

formally 19- and 21-valence-electron derivatives have

been studied and exploited for chemical applications.

Ligand exchange is also observed in the reaction of

manganocene adducts with dihalides MnX₂, leading to

binuclear halide-bridged [(MeC₅H₄)MnL₂X]₂(L ) PMe₃,

PEt₃, AsEt₃; X ) Cl, Br, I) or mononuclear complexes

(MeC₅H₄)MnL₂I (L₂) (PMe₃)₂, dmpe).¹⁴

On the basis of the facile cyclopentadienyl replace-

ment and the capability of adduct formation of manga-

nocenes, we sought to develop a new manganocene

chemistry by probing their reactions with terminal or

trimethyltin-substituted acetylenes in the presence of

dmpe.

manganocene and 1,1′-dimethylmanganocene react in

a 1:1 ratio with terminal and trimethyltin-substituted

alkynes R′CtCR′′ (R′ ) Ph, SiMe₃; R′′ ) H, SnMe₃) with

substitution of one five-membered ligand to form the

alkynyl complexes 1a ,b and 2a ,b (Scheme 1).

Long reaction times are required for the formation of

1a and 2a from terminal alkynes (1a , 20 h; 2a , 65 h),

and even longer times are needed for the reaction

starting from trimethyltin-substituted alkynes (1a , 30

h; 2a , 80 h). In the latter transformations the cyclopen-

tadienyl moieties are liberated as trimethyltin deriva-

tives, as proven by NMR spectroscopy (see Experimental

Section). The reverse reactionsformation of cyclopen-

tadienyl transition-metal complexes via cleavage of a

trialkyltin-cyclopentadienyl bondsis known for dia-

magnetic metal centers.¹⁵

The primary intermediates in these three-component

transformations are the dmpe adducts (RC₅H₄)₂Mn-

(dmpe), previously reported by Wilkinson et al.,¹⁰as

shown by ¹H NMR spectroscopic studies in C₆D₆. As the

dmpe ligand easily dissociates from this adduct (fast

exchange on the ¹H NMR time scale), manganocenes

are still present in the reaction mixture. The reaction

Resu lts a n d Discu ssion

Syn th eses an d P r oper ties of Half-San dwich Com -

p lexes (RC₅H₄)Mn (d m p e)(C≡CR′) (R ) H, Me; R′

) P h , SiMe₃; 1a ,b a n d 2a ,b). In the presence of dmpe

(13) Heck, J .; Massa, W.; Weinig, P. Angew. Chem. 1984, 96, 699;

Angew. Chem., Int. Ed. Engl. 1984, 23, 722.

(14) Ko¨hler, F. H.; Hebendanz, N.; Mu¨ller, G.; Thewalt, U. Organo-

metallics 1987, 6, 115.

(15) (a) Abel, E. W.; Moorhouse, S. J . Organomet. Chem. 1971, 29,

227. (b) Abel, E. W.; Dunster, M. O.; Waters, A. J . Organomet. Chem.

1973, 49, 287. (c) Abel, E. W.; Moorhouse, S. J . Chem. Soc., Dalton

Trans. 1973, 1706.

Mono- and Bis(alkynyl) Mn(II) and Mn(III) Complexes

Organometallics, Vol. 18, No. 8, 1999 1527

sequence of Scheme 1 can be initiated from the adduct

complexes and acetylenes, while no reaction is observed

between manganocenes and acetylenes in the absence

of dmpe, even under more forcing conditions. Therefore,

the multistep reaction obviously proceeds via the dmpe

adducts (RC₅H₄)₂Mn(dmpe), giving the half-sandwich

complexes 1a ,b and 2a ,b.

Rh(III) > Rh(II) > Rh(I)²⁰was derived. These findings

were interpreted in terms of enhanced π back-bonding

to the acetylide unit in low-oxidation-state species. In

certain cases oxidation of the metal center may have

no²¹or even a reverse^22-24effect on the stretching

frequency of the attached acetylide ligand, which is

inconsistent with the π back-bonding hypothesis, but a

suitable interpretation is still lacking.

NMR spectra of paramagnetic complexes may provide

useful information on their structures and electronic

states.²⁵To manganese complexes paramagnetic NMR

has been applied in just a few instances, e.g. to the

parent manganocenes and their substituted deriva-

tives.^3,6The chemical shifts of the methyl and methylene

protons of the dmpe ligands are especially suited for

assigning different spin states. For the high-spin com-

plexes (MeC₅H₄)Mn(dmpe)I¹⁴and Mn(dmpe)₂X₂(X ) Br,

I)²⁶two broad downfield signals are observed for the

methylene and the methyl groups of the dmpe ligand,

while for the low-spin complexes Mn(dmpe)₂X₂(X )

Me,²⁶CtCR′¹⁶) these resonances are shifted to higher

field strengths and the width at half-height of these

signals is much smaller. For the low-spin Mn(III) cations

[Mn(dmpe)₂(CtCR′)₂]⁺the upfield shift is even larger

and the half-widths are about twice as large due to the

presence of two unpaired electrons.¹⁶

At this stage of the reaction sequence the R ) H and

R ) Me derivatives behave differently. While the

complexes 1a and 2a (R ) Me) can be isolated in pure

form, the more reactive species 1b and 2b (R ) H) could

only be detected in solution. Their enhanced reactivity,

which parallels that of (C₅H₅)₂Mn(dmpe) (the reaction

of the latter with acetylenes proceeds faster than that

1

of (MeC₅H₄)₂Mn(dmpe), as shown by H NMR monitor-

ing in deuterated 1,2-dichloroethane), leads to further

cyclopentadienyl substitution, giving 3 and 4, respec-

tively (Scheme 1). Obviously, the unsubstituted cyclo-

pentadienyl ring is a better leaving group than the

methylcyclopentadienyl ring in the (RC₅H₄)₂Mn(dmpe)

adducts as well as in the (RC₅H₄)Mn(dmpe)(CtCR′)

complexes.

For this reaction sequence starting from (C₅H₅)₂Mn

the bis(alkynyl) bis(dmpe) complexes 3 and 4 are

seemingly the thermodynamic products. Presumably,

the same is valid for the complexes with MeC₅H₄, and

the isolation of 1a and 2a is only possible due to the

kinetic inertness of these compounds.

Our previous investigations in this field have dem-

onstrated that the bis(alkynyl)manganese complexes

Mn(dmpe)₂(CtCR′)₂(3, 4) undergo reversible 1-electron-

oxidation processes leading to 16-electron low-spin

cations.¹⁶To explore the general accessibility of organo-

metallic Mn(III) systems, we also examined the redox

chemistry of the mono(alkynyl) derivatives 1a and 2a .

The addition of 1 equiv of [(C₅H₅)₂Fe](BF₄) to 1a or 2a

resulted in the formation of the sensitive cationic species

[1a ](BF₄) and [2a ](BF₄), respectively (Scheme 1). The

complexes [1a ](BF₄) and [2a ](BF₄) were isolated in a

pure state and characterized by spectroscopic, electro-

chemical, and magnetic means.

In the ¹H NMR spectra of the (RC₅H₄)₂Mn(dmpe)

intermediates the chemical shifts of the signals of the

dmpe and RC₅H₄ligands were found close to those of

the above-mentioned high-spin complexes, indicating a

high-spin configuration for (RC₅H₄)₂Mn(dmpe) in solu-

tion consistent with the observed crystallographic bond

lengths and magnetic moments found in the solid

state.¹⁰

Despite the large line widths, which cause in some

cases overlap and integration problems, assignment of

1

all resonances in the H NMR spectra of 1a , 2a , [1a ]⁺,

and [2a ]⁺was possible. Due to the thermal instability

of these complexes, the temperature could not be

increased in order to induce sharpening of the signals.

The complexes 1a and 2a have approximately the same

The IR spectra of 1a and [1a ](BF₄), recorded in KBr

pellets, exhibit bands at 2008 and 2070 cm^-1, respec-

tively, a region characteristic of the phenylethynyl C_R-

C_âstretching mode.¹⁷The ν(CtC) absorptions of the

(trimethylsilyl)ethynyl derivatives are observed at much

lower wavenumbers (1945 cm^-1for 2a ; 1995 cm^-1for

[2a ](BF₄)), which appears to be a typical feature of

SiMe₃-substituted acetylide ligands and may suggest a

weakening of their triple bond.¹⁸The wavenumber of

the CtC absorption increases upon oxidation of the

metal center. The same observation was made for the

bis(alkynyl) derivatives 3 and 4 in the Mn(II) and

Mn(III) oxidation states¹⁶and also for compounds of the

general type [M(CtCR){E(CH₂CH₂PPh₂)₃}]ⁿ⁺(M ) Co,

Rh; E ) N, P), for which the ordering Co(III) > Co(II),¹⁹

(20) (a) Bianchini, C.; Meli, A.; Peruzzini, M.; Vacca, A.; Laschi, F.;

Zanello, P.; Ottaviani, F. M. Organometallics 1990, 9, 360. (b) Bian-

chini, C.; Laschi, F.; Ottaviani, F.; Peruzzini, M.; Zanello, P. Organo-

metallics 1988, 7, 1660. (c) Bianchini, C.; Masi, D.; Meli, A.; Peruzzini,

M.; Ramirez, J . A.; Vacca, A.; Zanobini, F. Organometallics 1989, 8,

2179. (d) Bianchini, C.; Mealli, C.; Peruzzini, M.; Vizza, F.; Zanobini,

F. J . Organomet. Chem. 1988, 346, C53. (e) Bianchini, C.; Meli, A.;

Peruzzini, M.; Zanobini, F. J . Chem. Soc., Chem. Commun. 1987, 971.

(f) Bianchini, C.; Meli, A.; Peruzzini, M.; Zanobini, F.; Zanello, P.

Organometallics 1990, 9, 241.

(21) (a) Bianchini, C.; Laschi, F.; Masi, D.; Ottaviani, F. M.; Pastor,

A.; Peruzzini, M.; Zanello, P.; Zanobini, F. J . Am. Chem. Soc. 1993,

115, 1175. (b) Bianchini, C.; Meli, A.; Peruzzini, M.; Frediani, P.;

Bohanna, C.; Esteruelas, M. A.; Oro, L. A. Organometallics 1992, 11,

138.

(22) Connelly, N. G.; Gamasa, M. P.; Gimeno, J .; Lapinte, C.; Lastra,

E.; Maher, J . P.; Le Narvor, N.; Rieger, A. L.; Rieger, P. H. J . Chem.

Soc., Dalton Trans. 1993, 2575, 2981 (correction).

(23) Bitcon, C.; Whiteley, M. W. J . Organomet. Chem. 1987, 336,

385.

(24) (a) Beddoes, R. L.; Bitcon, C.; Whiteley, M. W. J . Organomet.

Chem. 1991, 402, 85. (b) Adams, J . S.; Bitcon, C.; Brown, J . R.; Collison,

D.; Cunnigham, M.; Whiteley, M. W. J . Chem. Soc., Dalton Trans.

1987, 3049.

(25) (a) NMR of Paramagnetic Molecules; La Mar, G. N., Horrocks,

W. DeW., Holm, R. H., Eds.; Academic Press: New York, 1973. (b)

Bertini, I.; Luchinat, C. NMR of Paramagnetic Molecules in Biological

Systems; Benjamin-Cummings: Menlo Park, CA, 1986. (c) Bertini, I.;

Luchinat, C. Coord. Chem. Rev. 1996, 150.

(16) Krivykh, V. V.; Eremenko, I. L.; Veghini, D.; Petrunenko, I. A.;

Pountney, D. L.; Unseld, D.; Berke, H. J . Organomet. Chem. 1996, 511,

111.

(17) Manna, J .; J ohn, K. D.; Hopkins, M. D. Adv. Organomet. Chem.

1995, 38, 79.

(18) Sun, Y.; Taylor, N. J .; Carty, A. J . Organometallics 1992, 11,

4293.

(19) (a) Bianchini, C.; Innocenti, P.; Meli, A.; Peruzzini, M.; Zanobini,

F.; Zanello, P. Organometallics 1990, 9, 2514. (b) Bianchini, C.;

Peruzzini, M.; Vacca, A.; Zanobini, F. Organometallics 1991, 10, 3697.

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M.; Hursthouse, M. B. J . Chem. Soc., Dalton Trans. 1985, 1339.

1528 Organometallics, Vol. 18, No. 8, 1999

Unseld et al.

Sch em e 2. Equ ilibr iu m betw een 1, 2 a n d 3, 4

F igu r e 1. EPR spectrum of 1a in toluene at -190 °C.

dmpe chemical shifts as Mn(dmpe)₂(CtCR′)₂deriva-

tives,¹⁶but the signals of the former species are broader

(w_1/2(CH₃) ≈ 3370 Hz (1a ) and 1130 Hz (2a )). Analo-

gously, the range of the chemical shifts of the dmpe

signals of the cationic derivatives [1a ]⁺and [2a ]⁺are

close to those of the bis(alkynyl) cations [Mn(dmpe)₂-

(CtCR′)₂]⁺.¹⁶These findings indicate low-spin states for

both the neutral and the cationic derivatives in solution.

The low-spin character of 1a and 2a is confirmed by

their X-band EPR spectra. The solution EPR spectra

show broad singlets centered near g ) 2 at temperatures

above -100 °C. At liquid-nitrogen temperature toluene

glasses of both complexes give well-resolved and similar

EPR spectra. Figure 1 shows the EPR spectrum of 1a

in toluene at -190 °C. The parallel features (1:2:1

triplets) at the low- and high-field ends can be separated

from the perpendicular ones in the center: g ) 2.07,

g_|) 2.19, A(⁵⁵Mn, I ) ⁵/₂) ) 100 G and A(³¹P, I ) ¹/₂) )

25 G. These spectra are qualitatively similar to those

of other low-spin Mn(II) half-sandwich complexes²⁷and

different from those recorded for high-spin compounds.²⁶

The corresponding cationic Mn(III) complexes [1a ]⁺and

[2a ]⁺are EPR-silent.

th e Bin u clea r Com p lexes 7 a n d 8. The complexes 1a

and 2a are labile and show a great tendency to undergo

carbon-centered radical reactions as hydrogen abstrac-

tion or radical coupling. Both routes are competitive,

producing the mononuclear vinylidene complexes 5 and

6 or the binuclear bis(vinylidene) derivative 7 (Scheme

3).

The course of these transformations depends strongly

on the nature of R′ and the solvent, i.e., the ability of

any of the components to donate a hydrogen radical. For

the trimethylsilyl derivatives (R′ ) SiMe₃) dimerization

with C-C coupling comparable to the formation of 7

does not occur, which is presumably due to steric

shielding of the radical centers. Instead, complex 6 is

formed by hydrogen abstraction (Scheme 3). To probe

the role of the solvent as a H^•source, this reaction was

carried out in C₆D₆. Prolonged stirring of 2a in C₆D₆

results in the formation of nondeuterated 6 so that the

hydrogen atoms must originate from R′, MeC₅H₄, or the

phosphine moieties. For the phenyl derivative 1a both

pathways of Scheme 3 are available, giving a mixture

of the complexes 5 and 7.

When 1a or 2a is reacted with n-Bu₃SnH as H^•source,

the H^•scavenging products are formed in 83% (5) and

43% (6) yields, respectively (Scheme 4a). As byproducts

the SnBu₃-substituted vinylidene complexes (MeC₅H₄)-

Mn(dmpe)(dCdC(R′)SnBu₃) have been identified spec-

troscopically. A complete separation of these complexes

from the species 5 or 6 could not be achieved, neither

by fractional crystallization nor by chromatography. To

circumvent this byproduct formation, (C₅Me₅)Mo(CO)₃H

is applied as H^•source (Scheme 4b). In this case 1 and

2 are quantitatively and cleanly converted to 5 and 6,

respectively. This chemical selectivity may be due to the

known high recombination rate of [(C₅Me₅)Mo(CO)₃]^•

radicals.²⁸The complexes 5 and 6 may also be prepared

by reaction of (MeC₅H₄)Mn(η⁶-C₇H₈) with phosphines

and terminal alkynes.²⁹

Syn th eses of Bis(a lk yn yl)bis(d m p e)m a n ga n ese

Com p lexes Mn (d m p e)₂(CtCR′)₂(R′ ) P h , SiMe₃; 3,

4). Bis(alkynyl)bis(dmpe)manganese complexes 3 and

4 can be obtained from manganocene/acetylene/dmpe

reaction mixtures. For optimal yields it proved neces-

sary to apply the stoichiometric 1:2:2 ratio of the

starting components (Scheme 1). 3 and 4 thus generated

from manganocenes are spectroscopically and analyti-

cally identical with those isolated from the reaction of

Mn(dmpe)₂Br₂with lithiated acetylenes.¹⁶In the ab-

sence of dmpe and acetylene the pure complexes 1a and

2a tend to equilibrate with the bis(alkynyl)bis(dmpe)-

manganese species 3 and 4 and the corresponding

manganocene (Scheme 2). The final equilibriumsas

measured by ¹H NMR spectroscopy in C₆D₆sis reached

within several days (1a , 1a :3 ≈ 1:6, 12 days; 2a , 2a :4

≈ 1:7, 10 days).

5 and 6 can be oxidized to [1a ]⁺and [2a ]⁺by reaction

with stoichiometric amounts of [(C₅H₅)₂Fe](BF₄) under

H₂elimination. The cationic complexes are isolated as

Ra d ica l Rea ction s of 1a /2a a n d [1a ]⁺/[2a ]⁺: Syn -

th esis of th e Vin ylid en e Com p lexes 5 a n d 6 a n d

(28) Hugheys, J . L.; Bock, C. R.; Meyer, T. J . J . Am. Chem. Soc.

1975, 97, 4440.

(29) Krivykh, V. V.; Berke, H. Unpublished results.

(27) Pike, R. D.; Rieger, A. L.; Rieger, P. H. J . Chem. Soc., Faraday

Trans. 1989, 85, 391.

Mono- and Bis(alkynyl) Mn(II) and Mn(III) Complexes

Organometallics, Vol. 18, No. 8, 1999 1529

Sch em e 3. Com p etitive Rea ction of 1 a n d 2 To Give 5-7

Sch em e 4. Selective Rea ction of 1 a n d 2 To Give 5

a n d 6

Sch em e 5. Syn th esis of 8 fr om [1a ]⁺a n d Red ox

Rea ction s To Give 7

their tetrafluoroborate salts in 85% and 79% yields,

respectively.

The dimeric compound 7 (Scheme 3) is obtained only

in moderate yields due to the competition with the

hydrogen abstraction process but can be separated from

the vinylidene species 5 by fractional crystallization

from pentane. 5 cannot be isolated from this mixture

and is only detected spectroscopically.

The preparation of divinylidene-bridged complexes of

the general formula [L_nMdCdCR-CRdCdML_n]^m+(M

) Fe, Ru, Mo; R ) H, Me, n-Bu, Ph, SiMe₃; m ) 0, 1)

was reported earlier.^30,31All of them were formed via

dimerization of odd-electron complexes generated in

redox transformations. However, in situ generated or

isolable radicals [(C₅R₅)M(dppe)(CdC(H)R′)]⁺(M ) Fe,²²

Ru;²³R ) H, Me; R′ ) t- Bu, Ph) and [Mo(C H₇)(dppe)-

7

30d,e

(CtC-t- Bu)]⁺

are stable, demonstrating that the

course of such radical dimerizations depends on the

bulkiness of the organic substituents, the metal center,

and the ancillary ligands. Besides 1a , only one neutral

complex in these coupling series is known in the

literature;^30gall other processes are based on cationic

species. Obviously, the charge of the dimerizing species

is not an important factor, as long as the radical

character is sufficiently delocalized onto the â-carbon

atom. Indeed, [1a ]⁺slowly dimerizes to give the di-

Sch em e 6. F or m a l C-C Cou p lin g Rea ction of

Ca tion ic Mn (III) Acetylid e Com p lexes

(30) (a) Iyer, R. S.; Selegue, J . P. J . Am. Chem. Soc. 1987, 109, 910.

(b) Le Narvor, N.; Lapinte, C. J . Chem. Soc., Chem. Commun. 1993,

357. (c) Le Narvor, N.; Toupet, L.; Lapinte, C. J . Am. Chem. Soc. 1995,

117, 7129. (d) Beddoes, R. L.; Bitcon, C.; Ricalton, A.; Whitley, M. W.

J . Organomet. Chem. 1989, 367, C21. (e) Beddoes, R. L.; Bitcon, C.;

Grime, R. W.; Ricalton, A.; Whitley, M. W. J . Chem. Soc., Dalton Trans.

1995, 2873. (f) Bruce, M. I.; Cifuentes, M. P.; Snow, M. R.; Tiekink, R.

T. J . Organomet. Chem. 1989, 359, 379. (g) Lo¨we, C.; Hund, H.-U.;

Berke, H. J . Organomet. Chem. 1989, 372, 295.

cationic bis(carbyne) compound 8, which can be sepa-

rated from further decomposition products by crystal-

lization in about 20% yield (Scheme 5).

Since [1a ]⁺has to be considered a biradical, this

process can be envisaged to occur by coupling of triplet

carbene centers (Scheme 6). Alternatively, a formally

stepwise electron pairing via carbon-centered mono-

(31) Bruce, M. I. Chem. Rev. 1991, 91, 213.

1530 Organometallics, Vol. 18, No. 8, 1999

Unseld et al.

F igu r e 2. Variable-temperature ³¹P NMR spectra of 7 (at -70, -50, -30, -10, 10, 22, and 45 °C) and simulated spectra.

radicals as suggested in Scheme 6 could serve as a

model. Such coupling reactions of 16-VE complexes have

not been observed previously, but the principal struc-

tural type of such species, binuclear complexes contain-

ing a bis(carbyne) bridging unit, have already been

reported.³²8 can also be prepared in quantitative yield

by oxidation of 7 with 2 equiv of a ferrocenium salt

(Scheme 5). Rereduction can be accomplished by reac-

tion of 8 with methylcobaltocene (Scheme 5). Both

compounds 7 and 8 are thermally stable, and complex

8 is even air-stable. The IR spectrum of 7 shows two

medium-strong bands at 1562 and 1589 cm^-1in the

characteristic range for vinylidene ligands (but an

assignment is difficult due to the overlap with the Cd

C vibrations of the phenyl rings).³¹8 additionally

) PPh₃³⁵). Obviously the C_Rresonances in these com-

plexes shift to higher field strength upon substitution

of CO by phosphines.

The ³¹P{¹H} NMR spectrum of 8 displays a sharp,

temperature-independent singlet at 83.2 ppm, while for

7 the signal of the phosphorus nuclei at 95.6 ppm is

broadened at room temperature. At 203 K the spectrum

exhibits an AB quartet at 93.4 ppm (J _PP) 42.3 Hz).

When the temperature is raised, the components of the

AB system broaden and coalesce at 295 K (∆ν ) 246.5

Hz). By line shape analysis of the ³¹P NMR spectra of 7

at different temperatures the free energy of activation,

∆G^q, is evaluated as 56.7 kJ mol^-1for the two-site

exchange process (Figure 2). This barrier is attributed

to the hindered rotation around the MndC bond, and

it is significantly higher than the barriers in the

mononuclear complex 5 (∆G^q) 36.0 kJ mol^-1),²⁹in

[(C₅H₅)M(L-L)(dCHR)]⁺species (R ) H, Ph, M ) Fe,

L-L ) dppm, 41.0 kJ mol^{-1 36}and L-L ) dppe, 39.3

possesses a broad CdC absorption band at 1632 cm^-1

.

In the ¹³C NMR spectrum of 5 the resonance for the

C_Ratom appears as a triplet at 342.6 ppm (²J _PC) 35

Hz) substantially upfield from those of (MeC₅H₄)MnL₂-

(CdCPh₂) (L ) CO, 395.7 ppm; L ) PPhMe₂, 381.4

ppm³³). For comparison, the corresponding C_Rreso-

nances in carbyne complexes [(C₅H₅)MnLL′(tCPh)]⁺

appear at 356.9 (L ) L′ ) CO³⁴) and 343.7 (L ) CO, L′

kJ mol^{-1 37}M ) Ru, L-L ) dppe, 38.1 kJ mol^{-1 38}) and

;

even in the binuclear compound [(C₅H₅)₂Fe₂(dppe)₂(µ-

C₄Me₂)]²⁺(37 kJ mol^-1).^30a

For the iron and ruthenium complexes the horizontal

vinylidene ligand orientation (the CdCR₂vinylidene

(32) (a) Ustynyuk, N. A.; Vinogradova, N. V.; Andrianov, V. G.;

Stuchkov, Y. T. J . Organomet. Chem. 1984, 268, 73. (b) Krouse, S. A.;

Schrock, R. R. J . Organomet. Chem. 1988, 355, 257. (c) Shih, K.-Y.;

Schrock, R. R.; Kempe, R. J . Am. Chem. Soc. 1994, 116, 8804. (d)

Woodworth, B. E.; White, P. S.; Templeton, J . L. J . Am. Chem. Soc.

1997, 119, 828.

(35) Terry, M. R.; Kelley, C.; Lugan, N.; Geoffrey, G. L.; Haggarty,

B. S.; Rheingold, A. L. Organometallics 1993, 12, 3607.

(36) Gamasa, M. P.; Gimeno, J .; Lastra, E.; Martin, B. M.; Anillo,

A.; Tiripicchio, A. Organometallics 1992, 11, 1373.

(33) Schubert, U.; Gro¨nen, J . Chem. Ber. 1989, 122, 1237.

(34) Fischer, E. O.; Meineke, E. W.; Kreissl, F. R. Chem. Ber. 1977,

110, 1140.

(37) Consiglio, G.; Bangerter, F.; Darpin, C.; Morandini, F.; Lucchini,

V. Organometallics 1984, 3, 1446.

(38) Consiglio, G.; Morandini, F. Inorg. Chim. Acta 1987, 127, 79.

Mono- and Bis(alkynyl) Mn(II) and Mn(III) Complexes

Organometallics, Vol. 18, No. 8, 1999 1531

plane is perpendicular to the pseudo mirror plane

bisecting the (C₅H₅)ML₂moiety) was predicted theoreti-

cally³⁹and proven by crystallographic investigations.^36,40

Recently, the first examples of vertical orientations of

vinylidene ligands were reported for the mono- and

binuclear complexes [Mo(C₇H₇)(dppe)(dCdCHPh)]⁺and

[(Mo₂(C₇H₇)₂(dppe)₂(µ-C₄Ph₂)]^{2+ 30e}

.

From variable-temperature ¹H, ¹³C, and ³¹P NMR

spectra it can be deduced that the preferred orientation

of the vinylidene ligands in 5 and 7 is horizontal, as all

signals of 5 and 7 (R, R′, â, â′ of the cyclopentadienyl

ring (H, C); o-, m-H or o-, m-C of the phenyl ring and

other pairs of nuclei) are separated at low temperature

but coincide for both fragments of 7 at elevated tem-

perature. These observations confirm that the frozen

rotation of the vinylidene unit gives rise to signals of

two isomers containing diastereotopic H, C, and P

nuclei. The binuclear bis(vinylidene) complex 7 is

expected to have free or almost free rotation around the

central C-C bond, causing no isomerism based on this

motion.

X-r a y Diffr a ction Stu d ies on 2a , 5, 7 a n d 8.

Compounds 2a and 5 were subjected to X-ray structural

analyses, because 2a is a rare example of an organo-

metallic acetylide system with d⁵low-spin configuration

and it seemed to be intriguing to compare 2a with the

related electronically saturated vinylidene complex 5.

Significant structural changes might arise, as 2a is one

hydrogen atom deficient with respect to 5. The struc-

tures (Figure 3, Table 1) are compared on the basis that

the replacement of a trimethylsilyl group (2a ) by a

phenyl substituent (5) has only a minor influence.

The geometry around the manganese center in 2a is

pseudotetrahedral, which compares favorably with those

of related vinylidene complexes⁴²and also with com-

pound 5. The formal abstraction of H^•or R^•from a

vinylidene ligand does not give rise to severe structural

reorganization with respect to the P-Mn-P, P-Mn-

C, Cp′-Mn-C, and Cp′-Mn-P angles⁴¹(Table 1). The

Mn-C1 distance in 2a is approximately 0.2 Å larger

than that of 5 (Table 1), indicating that the vinylidene

moiety is a strong π-accepting ligand, while the acetylide

group of 2a behaves π-saturated in its interaction with

the metal center. This is also supported by the smaller

C-C distance of 2a , with triple-bond character, com-

pared to that of 5, exhibiting double-bond character

(Table 1). The complexes 2a and 5 are therefore well-

represented by the valence bond structures presented

in Schemes 1 and 3.

F igu r e 3. X-ray structures of 2a and 5.

Ta ble 1. Selected Bon d Dista n ces (Å) a n d An gles

(d eg) for Com p lexes 2a a n d 5⁴¹

2a

5

Mn-P1

Mn-P2

Mn-C1

C1-C2

Mn-Cp

2.2118(9)

2.212(1)

1.921(3)

1.226(4)

1.78(1)

2.204(2)

2.191(2)

1.731(5)

1.344(6)

1.79(1)

P1-Mn-P2

P1-Mn-C1

P2-Mn-C1

Mn-C1-C2

P1-Mn-Cp

P2-Mn-Cp

C1-Mn-Cp

83.22(3)

89.78(8)

87.2(1)

179.4(3)

127.4(4)

128.7(3)

126.2(4)

84.01(6)

90.9(2)

88.7(2)

178.2(5)

124.81(6)

128.93(6)

126.4(4)

vinylidene plane through C1-C2-C3 amounts to 74°,

and that between the plane through Cp2-Mn31-C31⁴¹

and the plane through C31-C32-C33 amounts to 79°.

In the iron dimer the corresponding angles are 90 and

117°,^30awhile in the molybdenum dimer the ligand

orientation approximates that of a vertical one with a

19° tilt.^30d,eThe C1-C2-C32-C31 torsional angle is

273.6(5)°, in contrast to a planar s-trans conformation

at the central C-C bond found in the iron and molyb-

denum dimers (torsional angle 0°). The phenyl rings are

only slightly rotated (16.8(4)°) from their ideal coplanar

position, allowing conjugation with the double bonds of

the vinylidene ligands. This leads to a shortening of the

C-C distances between the phenyl groups and the

vinylidene backbone and concomitantly to an increase

of the central C2-C32 bond length (Table 2) compared

to that in the molybdenum dimer with a planar bridging

carbon unit and almost perpendicular phenyl rings.

Other structural parameters of the Mn-C₄-Mn bis-

The molecular structures of 7 and 8 are illustrated

in Figure 4; selected bond lengths and angles are given

in Table 2. The binuclear complex 7 contains no center

of symmetry similar to the structure of the related dimer

[(C₅H₅)₂Fe₂(dppe)₂(µ-C₄Me₂)](BF₄)₂,^30ahowever, in con-

trast to the centrosymmetric dimer [Mo₂(C₇H₇)₂(dppe)₂-

(µ-C₄Ph₂)](PF₆)₂.^30d,eThe orientation of the vinylidene

ligand in both fragments is almost horizontal: the angle

41

between the plane through Cp1-Mn1-C1

and the

(39) (a) Schilling, B. E. R.; Hoffmann, R.; Lichtenberger, D. L. J .

Am. Chem. Soc. 1979, 101, 585. (b) Kostic, N. M.; Fenske, R. F.

Organometallics 1982, 1, 974.

(40) Miller, D. C.; Angelici, R. J . Organometallics 1991, 10, 79.

(41) Cp denotes the centroid of the cyclopentadienyl or methyl-

cyclopentadienyl ring.

(42) Bruce, M. I.; Swincer, A. G. Adv. Organomet. Chem. 1983, 22,

59.

1532 Organometallics, Vol. 18, No. 8, 1999

Unseld et al.

F igu r e 5. Cyclic voltammogram of 7 (10^-3M in 0.1 M

n-Bu₄NPF₆/CH₂Cl₂; vs Fc/Fc⁺; 0.4 V s^-1).

about the olefinic bridge. The Mn1-C1-C2-C2a-C1a-

Mn1a backbone forms a plane including the C3 and C3a

ipso carbon atoms of the phenyl substituents. The

phenyl rings are rotated by 68.2(2)° out of conjugation

with respect to the plane of the conjugated system. The

C2dC2a distance (Table 2) is slightly larger than that

of the related dimer (C₅H₅)₂Cr₂(CO)₄(µ-C₄Ph₂) (CdC )

1.375 Å^32a) and is significantly elongated compared to

that of (vinylcarbyne)manganese complexes [(C₅H₅)Mn-

(CO)₂(tCCHdCPh₂)]⁺(CdC ) 1.357 Å⁴³), [(C₅H₅)Mn-

(CO)(PPh₃)(tCCMedCPh₂)]⁺(CdC ) 1.357 Å³⁵), the

methyl-substituted dimer Tp′₂W₂(CO)₄(µ-C₄Me₂) (Tp′ )

hydridotris(3,5-dimethypyrazolyl)borate; CdC ) 1.36

Å^32d), and typical isolated (CdC ) 1.299 Å) and conju-

gated (CdC ) 1.330 Å) double bonds in organic mol-

ecules.⁴⁴This might be the result of enhanced crowding,

which is maximal in the binuclear derivative 8. The

lengthening of the MntC distance compared to that in

F igu r e 4. X-ray structures of 7 and 8.

Ta ble 2. Selected Bon d Dista n ces (Å) a n d An gles

(d eg) for Com p lexes 7 a n d 8⁴¹

7

8

Mn1-P1

2.188(2)

2.190(2)

1.742(5)

1.79(2)

1.351(6)

1.471(6)

1.529(6)

2.182(2)

2.183(2)

1.737(4)

1.79(2)

2.250(1)

2.275(1)

1.684(3)

1.79(2)

1.421(5)

1.486(5)

1.400(7)

Mn1-P2

Mn1-C1

Mn1-Cp1

C1-C2

C2-C3(Ph)

C2-C32

Mn31-P31

Mn31-P32

Mn31-C31

Mn31-Cp31

C31-C32

C32-C33(Ph)

(vinylcarbyne)manganese complexes (1.665-1.668 Å^35,43

)

is only marginal.

Cyclic Volta m m etr y, Nea r -IR, a n d EP R In vesti-

ga tion s on th e 7/8 Red ox Cou p le. As the complexes

7 and 8 can be reversibly converted by redox reagents,

we have studied the redox properties of 7 in more detail,

applying cyclic voltammetry (Figure 5). Two fully re-

versible redox couples are found at E_1/2) -0.656 and

1.353(6)

1.478(6)

P1-Mn1-P2

83.28(6)

91.5(2)

88.6(2)

84.47(5)

97.1(1)

119.7(5)

123.8(5)

125.1(7)

169.7(3)

P1-Mn1-C1

-0.445 V vs Fc/Fc⁺(∆E_p) 0.060-0.065 V and i_pa/i_pc

≈

P2-Mn1-C1

1 for scan rates of 0.050-0.500 V s^-1). The separation

of these waves amounts to 0.211 V, consistent with two

successive one-electron-oxidation steps, yielding the

monocation [7]⁺and the dication 8, respectively (Scheme

7).

P1-Mn1-Cp1

P2-Mn1-Cp1

C1-Mn1-Cp1

Mn1-C1-C2

P31-Mn31-P32

P31-Mn31-C31

P32-Mn31-C31

P31-Mn31-Cp31

P32-Mn31-Cp31

C31-Mn31-Cp31

Mn31-C31-C32

125.6(7)

130.1(7)

124.8(9)

177.4(4)

82.92(7)

90.7(1)

89.4(2)

Another pair of waves is observed at about 1.5 V

higher potentials, which can be assigned to the next

oxidation steps producing Mn(IV) derivatives. The first

wave (E_1/2) 0.945 V; ∆E_p) 0.065 V) is reversible at

high scan rates, but at values lower than 0.400 V s^-1

125.1(8)

130.1(7)

125.4(9)

177.4(4)

(vinylidene) moiety such as MndC and CdC distances

and MndCdC angles (Table 2) fall in a typical range.^31,42

The dicationic complex 8 possesses crystallographic

inversion symmetry, giving rise to a trans conformation

(43) Kolobova, N. E.; Ivanov, L. L.; Zhvanko, O. S.; Khitrova, O. M.;

Batsanov, A. S.; Struchkov, Y. T. J . Organomet. Chem. 1984, 262, 39.

(44) Allen, F. H.; Kennard, O.; Watson, D. G.; Brammer, L.; Orpen,

G.; Taylor, R. J . Chem. Soc., Perkin Trans. 2 1981, S1.

Mono- and Bis(alkynyl) Mn(II) and Mn(III) Complexes

Organometallics, Vol. 18, No. 8, 1999 1533

Sch em e 7. Red ox Tr a n sfor m a tion of 7, [7]⁺, a n d 8

F igu r e 6. EPR spectrum of 1a in dichloromethane at

-190 °C.

the intensity of the cathodic peak grows to give i_pa/i_pc

1. A similar situation exists for the wave at E_p1) 1.088

V, E_p2) 0.993 V (∆E_p) 0.095 V) at all scan rates

applied. These cathodic stripping peaks show that the

Mn(IV) derivatives precipitate on the working electrode.

The formal separation of these waves is less than in the

previous case (∆E ) 0.096 V). The magnitude of separa-

tions between formal redox potentials of binuclear

complexes is an indication of the strength of the

electronic interactions between the metal centers and

therefore is an important characteristic of the electronic

conductivity of the bridges.⁴⁵From the separation

between two one-electron steps the comproportionation

constant⁴⁶K_c1) 8 × 10³can be derived for the

equilibrium [Mn₂]⁰+ [Mn₂]²⁺a 2[Mn₂]⁺and K_c2) 77

(albeit thermodynamically not strictly correct, as the

redox processes are not reversible) for the equilibrium

[Mn₂]²⁺+ [Mn₂]⁴⁺a 2[Mn₂]³⁺. The former value sug-

gests a class II or class III behavior in the Robin-Day

nomenclature⁴⁷for the monocationic mixed-valence

complex [7]⁺; the latter shows that the mixed-valence

tricationic complex is only weakly coupled and is less

stable toward disproportionation.

<

F igu r e 7. Near-IR spectra of 7, [7]⁺, and 8 in dichloro-

methane.

M^-1cm^-1; ν_1/2≈ 3120 cm^-1; shoulder at ∼900 nm) in a

spectral range in which 7 and 8 are transparent (Figure

7). The bandwidth at half-height is smaller than ex-

pected from Hush’s theory⁴⁸for weakly coupled mixed-

valence compounds (ν_1/2≈ 4765 cm^-1) and is therefore

better assigned a transition between delocalized states

rather than an intervalence transition. This is in accord

with the conclusion drawn from the EPR measurement

and also conforms with the thermodynamic stability of

[7]⁺as determined from the CV measurement. The

observed splitting of this absorption band into at least

two components might be due to mixing with other

excited charge-transfer states, but a definitve assign-

ment is impossible at the moment.

The mixed-valence compound [7]⁺can be prepared by

oxidation of 7 (red) with 1 equiv of [(C₅H₅)₂Fe](BF₄), by

reduction of 8 (orange) with 1 equiv of (MeC₅H₄)₂Co, or

by comproportionation of equimolar amounts of 7 and

8. The resulting red-green solution has been analyzed

by EPR and near-IR spectroscopy. The EPR spectrum

(Figure 6) measured in a dichloromethane matrix at

-190 °C shows an undecet with broad individual lines

(g ≈ 2.018, A(⁵⁵Mn) ) 60 G). This pattern and the small

hyperfine coupling to the Mn centers (approximately

half of that of the mononuclear complexes 1a and 2a

and of other mononuclear low-spin manganese com-

pounds^16,27) points to an electron delocalization over

both Mn centers or a very rapid electron transfer (time

scale of the EPR method: 10⁸s^-1).

DF T Ca lcu la tion s on 7, [7]⁺, a n d 8. We have

perfomed density functional calculations on the com-

pounds [{(C₅H₅)Mn(PH₃)₂}₂(µ-C₄H₂)]ⁿ⁺(n ) 0-2; Scheme

8) modeling the complexes [{(MeC₅H₄)Mn(dmpe)}₂(µ-

C₄Ph₂)]ⁿ⁺(n ) 0, 7;, n ) 1, [7]⁺; n ) 2, 8).

The near-IR spectrum of [7]⁺shows an asymmetric

intense absorption band (λ ) 1018 nm; ꢀ ) 3.3 × 10³

The ground states, configurations, and energies of the

binuclear systems are given in Table 3 and the main

(45) Seyler, J . W.; Weng, W.; Zhow, Y.; Gladysz, J . A. Organo-

metallics 1993, 12, 3802.

(46) Creutz, C. Prog. Inorg. Chem. 1983, 30, 1.

(47) Robin, M. B.; Day, P. Adv. Inorg. Chem. Radiochem. 1967, 10,

247.

(48) (a) Hush, N. S.; Prog. Inorg. Chem. 1967, 8, 391. (b) Hush, N.

S. Coord. Chem. Rev. 1985, 64, 135.

1534 Organometallics, Vol. 18, No. 8, 1999

Unseld et al.

Sch em e 8. Bin u clea r Mod el Com p lexes

M-C σ-bonds, formed by the in- and out-of-phase d_σ

orbitals of the metal fragments interacting with the sp

hybrid orbitals of the terminal carbon atoms (1σ_uand

1σ_g), (ii) levels originating from the interactions of the

π donor orbitals (1π_uand 1π_g) of the ligand with the π_v

combinations forming the M-C π-bonds, and (iii) orbit-

als composed of the π acceptor orbitals (1p_uand 1p_g) of

the ligand and the appropriate combinations of two π_h

metal fragment orbitals with metal-vinylidene π back-

bonding character. π back-bonding is much stronger into

the 1p_uand 1p_gorbitals of the ligand than into the 2π_u

or 2π_gantibonding orbitals, an observation which has

already been made for mononuclear (C₅H₅)ML₂(CCH₂)

complexes.^39b

Ta ble 3. Electr on ic Sta tes, Com p lex

Con figu r a tion s, a n d En er gies (w ith Resp ect to

Atom s) for th e Mod el Com p lexes

[{(C₅H₅)Mn (P H₃)₂}₂(µ-C₄H₂)]^{n +}(n ) 0-2)

n

state

complex confign

energy/eV

The multiplicity of the Mn-C bonds is between 2 and

3, allowing for a facilitated rotation around this bond

(Scheme 8). The calculated energy difference between

horizontal and vertical conformations amounts to 49 kJ

mol^-1for the neutral binuclear model complex, with the

horizontal orientation of the vinylidene unit being more

stable. The preference of the horizontal position has

already been predicted by calculations on mononuclear

(C₅H₅)ML₂(CCH₂) complexes^39band confirmed by X-ray

structural analyses. The energy difference between

these binuclear conformers is about twice as large as

that calculated for the corresponding mononuclear

complex (C₅H₅)Mn(PH₃)₂(CCH₂) (24 kJ mol^-1), in good

agreement with the trend of the activation barriers

observed experimentally (vide supra).

0

1

2

¹A

²A

¹A

(64a)²(65a)²

(64a)²(65a)¹

(64a)²(65a)⁰

-243.08

-238.14

-229.45

Ta ble 4. Ma in Op tim ized Geom etr ica l P a r a m eter s^a

of [{(C₅H₅)Mn (P H₃)₂}₂(µ-C₄H₂)]^{n +}(n ) 0-2)^b)

n ) 0

n ) 1

n ) 2

Mn-P¹

Mn-P²

Mn-C¹

2.198/2.201

2.200/2.197

1.749/1.750

1.322/1.322

1.465

2.233/2.232

2.232/2.233

1.694/1.694

1.358/1.359

1.422

2.271/2.267

2.268/2.270

1.650/1.649

1.394/1.394

1.375

C

^1-C³

^3-C⁴

P¹-Mn-P²

P¹-Mn-C¹

P²-Mn-C¹

Mn-C¹-C³

C¹-C³-C⁴

91.3/91.4

93.1/93.1

94.0/94.1

93.0/93.5

93.6/92.9

179.2/179.3

122.5/122.5

90.4/90.1

91.2/91.3

90.1/89.7

91.3/91.2

179.3/178.2

125.3/126.3

179.1/179.0

124.2/124.2

The solid-state structure of 7, especially the torsional

angle of the C₄backbone (Scheme 8), deserves further

comment. A conformational analysis of a rotation around

the central C³-C⁴bond shows an energy minimum at

a torsional angle of 181.4° for the conformers in which

the {(C₅H₅)Mn(PH₃)₂} fragments are approximately

related by an inversion center in the 180° conformer

(Scheme 10, upper graph, conformers A; Table S4 of the

Supporting Information). Rotation of one {(C₅H₅)Mn-

(PH₃)₂} fragment around the Mn-C bond by 180° gives

a conformer in which the {(C₅H₅)Mn(PH₃)₂} fragments

are related by a mirror plane in the 180° conformer

(Scheme 10, lower graph, conformers B; Table S4 of the

Supporting Information). In the conformers of the B

series the 137 and 219° torsion angles are energetically

C¹-C³-C⁴-C²

181.4

179.9

180.1

a

b

Distances in Å and angles in deg. The first number refers to

the Mn¹moiety and the second to the Mn²fragment.

geometrical parameters in Table 4. The general elec-

tronic features of the metal fragment {(C₅H₅)Mn(PH₃)₂}

as well as the bonding to vinylidene fragments {:CdCH₂}

39b

in mononuclear complexes were described earlier.

Our calculations are in full agreement with these

results; therefore, our description of the bonding will

be restricted to those points essential for the binuclear

situation. The important four metal fragment orbitals

(π_v-σ; Scheme 9, Table S1 of the Supporting Informa-

tion) are mainly localized on the metal center and are

essentially composed of its 3d orbitals. The π_vorbitals

can π-donate in the vertical (yz) plane, whereas the

HOMO π_hcan π-donate in the horizontal (xy) plane. The

ligand fragment {:C¹dC³(H)C⁴(H)dC²:} may be viewed

as containing sp- (C¹and C²) and sp²-hybridized carbon

atoms (C³and C⁴) with double bonds between C¹/C³and

C²/C,⁴respectively. Its important orbitals (Scheme 9,

Table S2 of the Supporting Information) are the π

bonding orbitals (1π_uand 1π_g), the vacant π type p

orbitals of the ligating carbon atoms C¹and C²(1p_uand

1p_g), the π antibonding orbitals (2π_uand 2π_g), and the

σ type sp orbitals (1σ_uand 1σ_g).

The electronic interaction between the C₄H₂bridging

unit and the metal fragments will be discussed by

considering a fragment approach in which two {(C₅H₅)-

Mn(PH₃)₂} fragments interact with a C₄H₂species

(Table S3 of the Supporting Information). Scheme 9

shows the orbital interaction diagram of [{(C₅H₅)Mn-

(PH₃)₂}₂(µ-C₄H₂)]⁰. The interaction between the metal

fragments and the bridging ligand can be divided into

three groups: (i) two low-lying orbitals describing the

favored over the 180° torsion angle by some 17 kJ mol^-1

.

The absolute minimum, however, corresponds to the A

conformer with a 180° torsion angle. To answer the

question whether this discrepancy with the experimen-

tal structure (approximately conformer B with a 273.6°

torsional angle, vide supra) arises from electronic, steric,

or crystal-packing forces, we investigated first the

interaction of the phenyl rings attached to the C₄chain

with the CdC double bonds of the bridging ligand.

Calculations on the two conformations of H₂CdC(Ph)C-

(Ph)dCH₂show that the twisted chain with coplanar

phenyl groups, which should allow conjugation of the

phenyl groups with the double bonds of the vinylidene

ligand, is destabilized by 11 kJ mol^-1compared to the

planar C₄chain with orthogonal phenyl groups (Table

S4 of the Supporting Information). Therefore, electronic

reasons can be excluded. Explicit DFT calculations on

the two complex conformers, including the phenyl rings

[{(C₅H₅)Mn(PH₃)₂}₂(µ-C₄Ph₂)]⁰, have been carried out

which show that indeed the C₄chain twisted structure

Mono- and Bis(alkynyl) Mn(II) and Mn(III) Complexes

Organometallics, Vol. 18, No. 8, 1999 1535

Sch em e 9. Or bita l In ter a ction Dia gr a m of 7

with coplanar phenyl rings is preferred over the planar

C₄backbone and orthogonal phenyl groups by 31 kJ

mol^-1(Table S4 of the Supporting Information). Obvi-

ously, intramolecular steric crowding compensates and

even surpasses the electronic preference of the planar

C₄chain and the conformation found in the solid state

is neither a consequence of electronic conjugation of the

phenyl groups with the vinylidene double bonds nor a

crystal packing effect but an intramolecular steric effect.

For the model compounds of both oxidized complexes

[7]⁺and 8 the preferred conformation is that with a 180°

C¹C³C⁴C²torsion angle, in accordance with the X-ray

structural analysis for 8 (vide supra). The energetic

difference between the A and B 180° isomers is small

(<2 kJ mol^-1). Obviously, the twisting of the C₄chain

is electronically unfavorable. The interaction diagram

(Scheme 9) shows that removing one or two electrons

from the HOMO of the neutral complex reduces the π

antibonding interaction between the central carbon

atoms C³and C⁴, resulting in an increased double-bond

character which prohibits a facile rotation around this

bond. In addition the π bonding interaction between C¹/

C³and C²/C⁴as well as the π antibonding metal ligand

interaction is reduced giving rise to elongated C¹-C³

and C²-C⁴and shortened Mn-C bonds, respectively

(Table 4). Therefore, the neutral complex is best de-

scribed as a bis(vinylidene) complex and the dicationic

one as a bis(carbyne) species. The calculated bond

distances agree reasonably well with the experimental

ones; especially the decreasing of the Mn^1,2-C^1,2and the

central C³-C⁴bond lengths and the increasing of the

C¹-C³and C²-C⁴bond lengths on oxidizing the complex

is reproduced (Tables 2 and 4). The average deviation

for all Mn-L bond lengths of 7/[{(C₅H₅)Mn(PH₃)₂}₂(µ-

C₄H₂)]⁰and 8/[{(C₅H₅)Mn(PH₃)₂}₂(µ-C₄H₂)]²⁺is less

than 2%. Differences between calculated and experi-

mental atom distances within the C₄backbone (2-4%)

might be ascribed to the steric crowding imposed by the

additional phenyl groups attached to the C₄backbone,

which is corroborated by a comparison of calculated

bond lengths of the stable conformer [{(C₅H₅)Mn(PH₃)₂}₂-

(µ-C₄Ph₂)]⁰(Table S4 of the Supporting Information)

with those of 7 (calcd/exptl C¹-C³1.345, 1.348/1.351,

1.353 Å; C²-C⁴1.508/1.529 Å).

Broken-symmetry calculations on the model complex

[{(C₅H₅)Mn(PH₃)₂}₂(µ-C₄H₂)]⁺of the mixed-valent spe-

cies [7]⁺in various conformations (vide supra) all

converged into essentially symmetric structures, i.e.,

with equivalent metal sites and with Mn-C and C-C

bond lengths intermediate between those of the neutral

and the dicationic species (Table S4 of the Supporting

Information). The spin density is mainly and almost

equally concentrated on the manganese centers (0.3612

and 0.3606). An appreciable amount is also found on

the central carbon atoms of the C₄backbone (0.1581 and

0.1582, respectively), while less spin density is located

1536 Organometallics, Vol. 18, No. 8, 1999

Sch em e 10. Con for m a tion a l An a lysis of 7

Unseld et al.

on the ligating carbon atoms (0.0280 and 0.0281,

respectively). Therefore, both the geometrical param-

eters and the spin distribution indicate a symmetric

electronic configuration, i.e., that the odd electron is

delocalized between the two manganese centers in

accord with the EPR measurements of [7]⁺(vide supra).

Theoretically a quantitative estimate of the metal-

metal interaction in binuclear complexes may be ob-

tained from the difference between the first and second

gas-phase ionization potentials, ∆IP ) IP(n ) 1) - IP(n

) 0) (n ) charge of the complex). The ionization

potentials can be obtained via DFT calculations as the

difference in total energy between the reduced species

in the un-ionized initial state and the ionized final

state.⁴⁹With the calculated total energies E(n ) 0) )

-243.08 eV, E(n ) 1, geometry of n ) 0 complex) )

-237.95 eV and E(n ) 2, geometry of n ) 1 complex) )

-229.23 eV the ionization potentials were found to be

IP(n ) 0) ) E(n ) 1) - E(n ) 0) ) 5.13 eV and IP(n )

1) ) E(n ) 2) - E(n ) 1) ) 8.72 eV and accordingly

∆IP ) 3.59 eV. To correlate these theoretical gas-phase

values with the experimentally observable oxidation

potentials, especially the difference between the first

and second oxidation potentials ∆E°, the solvation

energies of the charged complexes has to be taken into

account. The solvation energies can roughly be esti-

mated using a simple electrostatic continuum model

derived by Onsager and Born.⁵⁰The solvation energy

is the sum of a dipole (∆E_solv,µ) and a charge (∆E_solv,Q

)

term: ∆E_solv) ∆E_solv,µ+ ∆E_solv,Q(the full expressions

are given, for example, in ref 51). The dipole moments

µ were calculated via a DFT calculation; the effective

cavity radius a₀was calculated as the sum of the

greatest internuclear distance plus the van der Waals

(50) (a) Born, M. Z. Phys. 1920, 1, 45. (b) Onsager, L. J . Am. Chem.

Soc. 1936, 58, 1486. (c) Rashin, A. A.; Honig, B. J . Phys. Chem. 1985,

89, 5588.

(49) Belanzoni, P.; Re, N.; Sgamellotti, A.; Floriani, C. J . Chem. Soc.,

Dalton Trans. 1998, 1825.

(51) Bickelhaupt, F. M.; Ziegler, T.; von Rague´ Schleyer, P. Or-

ganometallics 1995, 14, 2288.

Mono- and Bis(alkynyl) Mn(II) and Mn(III) Complexes

Organometallics, Vol. 18, No. 8, 1999 1537

set was employed for the 3s, 3p, 3d, 4s, and 4p valence orbitals

of manganese. For carbon (2s, 2p), phosphorus (3s, 3p), and

hydrogen (1s) use was made of a double-ú basis set augmented

by an extra polarization function. The fully occupied inner

shells of manganese and phosphorus (1s2s2p), as well as

carbon (1s), were assigned to the cores and treated by the

frozen-core approximation. All the geometries were calculated

at the local density approximation (LDA) level⁵⁹with the

parametrization of Vosko et al.⁶⁰The relative energies were

evaluated by including Becke’s nonlocal exchange⁶¹and Per-

dew’s nonlocal correlation corrections.⁶²All geometries were

fully optimized at the quantum mechanical level without

symmetry constraints. For the mixed-valence cation a broken-

symmetry spin-unrestricted calculation with an unsymmetri-

cal start-up potential was employed to avoid the problem of a

constrained equal amplitude of molecular orbitals over the two

metal centers and to allow the unpaired electron to localize

on one center if such an arrangement is energetically favor-

able.

Gen er a l P r oced u r e for t h e P r ep a r a t ion of St a n n yl-

a ted Acetylen es RCtSn Me₃(R ) P h , SiMe₃). In a Schlenk

tube equipped with a sintered-glass frit RCtCH (21 mmol)

was dissolved in diethyl ether (20 mL). After the solution was

cooled to -50 °C, a solution of n-BuLi in hexane (20.5 mmol)

was added dropwise. The cooling bath was removed, and the

mixture was allowed to reach room temperature. The resulting

solution was stirred for an additional 30 min. This solution

was again cooled to -30 °C, followed by addition of small

portions of Me₃SnCl (20 mmol) as a solid. A white fluffy solid

precipitated immediately. The resulting suspension was warmed

to room temperature and stirred for an additional 1 h. The

solvent was removed in vacuo until an oily suspension formed.

This residue was extracted with pentane, and the extract was

filtered through the glass frit. Evaporation of the solvent gave

the pure stannylated acetylene RCtCSnMe₃in good yields (R

) Ph, 85%; R ) SiMe₃, 89%).

radii of the two atoms involved (a₀) 15.3 Å). The

expressions were evaluated using the relative dielectric

constant of CH₂Cl₂(ꢀ_r) 9.08 at 20 °C), giving an

approximate solvation energy contribution of ca. -3.4

eV. This leads to a ∆E° value of ∼0.2 V, which is

surprisingly close to the experimental value of 0.211 V.

The relatively small ∆E° is therefore the result of a large

negative solvation energy of the charged species and is

not indicative of electron localization.

Exp er im en ta l Section

Reagent grade benzene, toluene, pentane, diethyl ether, and

tetrahydrofuran were dried and distilled from sodium benzo-

phenone ketyl prior to use. Dichloromethane was distilled first

from P₄O₁₀and, prior to use, from CaH₂. Literature procedures

were used to prepare the following compounds: 1,2-bis(di-

methylphosphino)ethane (dmpe),⁵²(RC₅H₄)₂Mn (R ) H, Me),⁵³

(MeC₅H₄)₂Mn(dmpe),¹⁰[(C₅Me₅)Mo(CO)₃H].⁵⁴PhCtCSnMe₃

and Me₃SiCtCSnMe₃were prepared by a modified literature

procedure⁵⁵(see the general procedure given below). n-BuLi

(1.6 M in hexane) and Me₃SiCtCH were used as received;

PhCtCH was freshly distilled before use. All the manipula-

tions were carried out under a nitrogen atmosphere using

Schlenk techniques or a drybox.

IR spectra were obtained on a Bio-Rad FTS-45 instrument

and near-IR spectra on a Perkin-Elmer Lambda 19 UV/vis/

near-IR spectrometer. NMR spectra were obtained on Varian

Gemini-300 or Varian Gemini-200 spectrometers at 300 or 200

MHz for ¹H, 75.4 or 50.3 MHz for ¹³C{¹H}, 121.5 MHz for

³¹P{¹H}, and 111.9 MHz for ¹¹⁹Sn{¹H} spectra, respectively.

The ¹H NMR spectra of paramagnetic compounds were ob-

tained from concentrated solutions of analytically pure com-

pounds using NMR tubes (5 mm) equipped with a J . Young

valve to ensure long-term exclusion of oxygen and moisture.

The assignment of the ¹H NMR signals for paramagnetic

compounds is principally based on the investigations of Ko¨hler

et al.^6,14Chemical shifts for ¹H and ¹³C{¹H} NMR spectra are

given in ppm with respect to the signals of residual solvent

protons (¹H) or ¹³C atoms of the deuterated solvents. ³¹P{¹H}

NMR spectra and ¹¹⁹Sn{¹H} NMR spectra were referenced to

85% external H₃PO₄and external (CH₃)₄Sn, respectively. (w_1/2

(1,2-Bis(d im et h ylp h osp h in o)et h a n e)(η⁵-m et h ylcyclo-

p en ta d ien yl)(p h en yleth yn yl)m a n ga n ese(II) (1a ). F r om

(MeC₅H₄)₂Mn , d m p e, a n d P h CtCH. (MeC₅H₄)₂Mn (215 mg,

1.01 mmol) was dissolved in 5 mL of benzene. To the resulting

red solution was added dmpe (150 mg, 1 mmol). The reaction

mixture turned pale yellow. Phenylacetylene (102 mg, 1 mmol)

was then added in one portion, and the mixture was stirred

for 20 h. The deep red solution was evaporated to dryness.

After extraction of the crude residue with pentane the solution

was filtered through Celite and concentrated. Crystallization

at -35 °C gave 211 mg of 1a (54% yield) as red-brown crystals.

¹H NMR (C₆D₆): δ -20.4 (w_1/2) 3370 Hz, PCH₃), -13.5

(PCH₂), -5.6 (w_1/2) 587 Hz, C₅H₄), 5.6 (w_1/2) 372 Hz, Ph H),

21.2 (w_1/2) 813 Hz, Ph H). IR (KBr): ν 2008, 1980 cm^-1(CtC).

EI-MS: m/z 386 (M⁺). Anal. Calcd for C₂₀H₂₈MnP₂: C, 62.34;

H, 7.33. Found: C, 62.46; H, 7.24.

) line width at half-height, vt ) virtual triplet, J _PH) ²J _PH

+

⁴J _PH; J _PC) J _PC+ J _PC). Mass spectra were obtained with a

Finnigan MAT 8430 instrument (EI and FAB) or a triple-stage

Finnigan TSQ 700 quadrupole instrument (San J ose, CA),

equipped with a combined Finnigan atmospheric pressure ion

(API) source (ESI). Cyclic voltammogramss were obtained with

a BAS 100B/W instrument (10^-3M in 0.1 M CH₂Cl₂/n-Bu₄N-

(PF₆)). X-band EPR spectra were obtained with a Varian E-6

spectrometer.

1

3

Com p u ta tion a l Deta ils. The calculations were carried out

using the Amsterdam density functional (ADF Version 2.2.1)

package developed by Baerends et al.⁵⁶and vectorized by

Ravenek.⁵⁷The adopted numerical integration procedure was

that of te Velde et al.⁵⁸An uncontracted triple-ú STO basis

Fr om (MeC₅H₄)₂Mn ,dm pe,an d P h CtCSn Me₃.(MeC₅H₄)₂-

Mn (108.7 mg, 0.51 mmol) was dissolved in 3 mL of benzene.

To the resulting red solution was added dmpe (75 mg, 0.5

mmol). The reaction mixture turned pale yellow. PhCtCSnMe₃

(132.5 mg, 0.5 mmol) was then added in one portion, and the

mixture was stirred for 38 h. The deep red solution was

evaporated to dryness. After extraction of the crude residue

with pentane the solution was filtered through Celite and

concentrated. Crystallization at -35 °C gave 41 mg of 1a (21%

yield) as red-brown crystals. The stannylated methylcyclopen-

tadiene byproduct was identified as 1-methyl-1-(trimethyl-

(52) Burt, R. J .; Chatt, J .; Hussain, W.; Leigh, G. J . J . Organomet.

Chem. 1979, 182, 203.

(53) Brauer, G. Handbook of Preparative Inorganic Chemistry; F.

Enke: Stuttgart, Germany, 1981; Vol. III.

(54) Nolan, S. P.; Laudrun, J . T.; Hoff, C. D. J . Organomet. Chem.

1985, 282, 357.

(55) (a) Dallaire, C.; Brook, M. A. Organometallics 1993, 12, 2332.

(b) Brandsmer, L. Preparative Acetylenic Chemistry, 2nd ed.; 1988. (c)

Stille, J . K.; Simpson, J . H. J . Am. Chem. Soc. 1987, 109, 2138.

(56) Baerends, E. J .; Ellis, D. E.; Ros, P. Chem. Phys. 1973, 2, 41.

(57) Ravenek, W. In Algorithms and Applications on Vector and

Parallel Computers; te Riele, H. J . J ., Decker, T. J ., van de Vorst, H.

A., Eds.; Elsevier: Amsterdam, 1987.

1

silyl)cyclopentadiene by ¹H and ¹¹⁹Sn NMR spectroscopy. H

NMR (C₆D₆): δ -0.086 (s, 9H, Sn(CH₃)₃, ²J _SnH) 52.3 Hz), 2.08

(59) Gunnarson, O.; Lundquist, I. Phys. Rev. 1974, B10, 1319.

(60) Vosko, S. H.; Wilk, L.; Nusair, M. Can. J . Phys. 1980, 58, 1200.

(61) Becke, A. D. Phys. Rev. A 1988, 38, 2398.

(58) (a) Boerritger, P. M.; te Velde, G.; Baerends, E. J . Int. J .

Quantum Chem. 1987, 33, 87. (b) te Velde, G.; Baerends, E. J . J .

Comput. Phys. 1992, 99, 84.

(62) Perdew, J . P. Phys. Rev. Lett. 1985, 55, 1655. (b) Perdew, J . P.

Phys. Rev. B 1986, 33, 8822. (c) Perdew, J . P.; Wang, Y. Phys. Rev. B

1986, 33, 8800.

1538 Organometallics, Vol. 18, No. 8, 1999

Unseld et al.

(s, 3H, C₅H₄CH₃), 5.64 (s, 2H, CH, J _SnH) 27.1 Hz), 5.77 (s,

2H, CH, J _SnH) 21.7 Hz); coupling to the different tin isotopes

¹¹⁷Sn and ¹¹⁹Sn is not resolved, and coupling constants are

therefore given as an average. ¹¹⁹Sn{¹H} NMR (C₆D₆): δ 30.3

(s, Sn(CH₃)₃).

(1,2-Bis(dimethylphosphino)ethane)(η⁵-methylcyclopenta-

dien yl)((tr im eth ylsilyl)eth yn yl)m an gan ese(II) (2a). Fr om

(MeC₅H₄)₂Mn , d m p e, a n d Me₃SiCtCH. (MeC₅H₄)₂Mn (234

mg, 1.1 mmol) was dissolved in 5 mL benzene. To the resulting

red solution dmpe (150 mg, 1 mmol) was added. The color of

the reaction mixture turned pale yellow. Trimethylsilylacetyl-

ene (100 mg, 1.02 mmol) was then added in one portion. The

solution was stirred for 65 h. The orange-red colored solution

was evaporated to dryness and the crude residue was extracted

with pentane. Filtration through Celite, concentrating the

solution and crystallization at -35 °C gave 275 mg 2a (65%

yield) as yellow-brown crystals. ¹H NMR (C₆D₆): δ -21.2 (w_1/2

diethyl ether (3 × 3 mL). Removal of the solvent gave 30 mg

of [2a ](BF₄) (90% yield) as a brownish powder. ¹H NMR (CD₂-

Cl₂): δ -50.1 (w_1/2) 453 Hz, PCH₂), -42.5 (w_1/2) 340 Hz,

PCH₃), -39.1 (w_1/2) 433 Hz, PCH₂), -28.8 (w_1/2) 306 Hz,

MeC₅H₄-2/5), -21.6 (w_1/2) 273 Hz, PCH₃), 7.8 (w_1/2) 95 Hz,

MeC₅H₄-3/4), 11.9 (w_1/2) 71 Hz, Si(CH₃)₃), 60.6 (w_1/2) 406

Hz, CH₃C₅H₄). IR (KBr)): ν 1995 cm^-1(CtC). ESI-MS: m/z

381 (M⁺). Anal. Calcd for C₁₇H₃₂BF₄MnP₂Si: C, 43.61; H, 6.89.

Found: C, 43.53; H, 6.46.

Red u ction of [1a ](BF ₄). To a cooled solution (-50 °C) of

[1a ](BF₄) (47 mg, 0.1 mmol) in 5 mL of dichloromethane was

added (MeC₅H₄)₂Co (21 mg, 0.1 mmol) as a solid. The mixture

was stirred for 3 h at the same temperature and was then

evaporated to dryness. The residue was extracted with pentane

(3 × 1 mL), filtered through Celite, and concentrated. The

filtrate was cooled to -80 °C to give 35 mg of 1a (89% yield)

as red-brown crystals. Spectroscopic and analytical data were

identical with those obtained by the synthesis from (MeC₅H₄)₂-

Mn and phenylacetylene/dmpe as described above.

) 1130 Hz, PCH₃), -13.4 (w_1/2) 654 Hz, PCH₂), -5.1 (w_1/2

)

380 Hz, C₅H₄), 5.6 (w_1/2) 165 Hz, Si(CH₃)₃). IR (KBr): ν 1945

cm^-1(CtC). EI-MS: m/z 381 (M⁺). Anal. Calcd for C₁₇H₃₂

-

Red u ction of [2a ](BF ₄). The reduction was carried out as

described above using [2a ](BF₄) (25 mg, 0.05 mmol) and

(MeC₅H₄)₂Co (11 mg, 0.05 mmol) in 3 mL of dichloromethane

to yield 15 mg of 2a (80% yield) as yellow-brown crystals.

Spectroscopic and analytical data were identical with those

obtained by the synthesis from (MeC₅H₄)₂Mn and (trimethyl-

silyl)acetylene/dmpe as described above.

MnP₂Si: C, 53.53; H, 8.46. Found: C, 53.46; H, 8.11.

F r om (MeC₅H₄)₂Mn , d m p e, a n d Me₃SiC≡CSn Me₃. (Me-

C₅H₄)₂Mn (108.7 mg, 0.51 mmol) was dissolved in 3 mL of

benzene. To the resulting red solution was added dmpe (72

mg, 0.48 mmol). The reaction mixture turned pale yellow.

Me₃SiCtCSnMe₃(125.3 mg, 0.48 mmol) was then added in

one portion. The solution was stirred for 80 h. The orange-red

solution was evaporated to dryness, and the crude residue was

extracted with pentane. Filtration through Celite, concentra-

tion of the solution, and crystallization at -35 °C gave 68 mg

of 2a (37% yield) as yellow-brown crystals.

(1,2-Bis(d im eth ylp h osp h in o)eth a n e)(η⁵-cyclop en ta d i-

en yl)(p h en yl-a lk yn yl)m a n ga n ese(II) (1b). This complex

was prepared in solution by starting from (C₅H₅)₂Mn, dmpe,

and PhCtCH and was identified by ¹H NMR spectroscopy.

¹H NMR (1,2-CD₂ClCD₂Cl): δ -20.6 (w_1/2) 850 Hz, PCH₃),

-13.3 (PCH₂), -5.7 (w_1/2) 348 Hz, C₅H₅), 5.3 (Ph H), 21.0

(Ph H).

(1,2-Bis(d im eth ylp h osp h in o)eth a n e)(η⁵-cyclop en ta d i-

en yl)((tr im eth ylsilyl)eth yn yl)m a n ga n ese(II) (2b). This

complex was prepared in solution by starting from (C₅H₅)₂-

Mn, dmpe, and Me₃SiCtCH and was identified by ¹H NMR

spectroscopy. ¹H NMR (1,2-CD₂ClCD₂Cl): δ -20.9 (w_1/2) 946

Hz, PCH₃), -13.2 (w_1/2) 542 Hz, PCH₂), -5.2 (w_1/2) 304 Hz,

C₅H₅), 5.3 (w_1/2) 136 Hz, Si(CH₃)₃).

Bis(1,2-b is(d im e t h ylp h osp h in o)e t h a n e )b is(p h e n yl-

eth yn yl)m a n ga n ese(II) (3). F r om (C₅H₅)₂Mn , d m p e, a n d

P h CtCH. A mixture of (C₅H₅)₂Mn (93 mg, 0.5 mmol), dmpe

(150 mg, 1 mmol), and PhCtCH (60 mg, 1.18 mmol) in 20 mL

of benzene was stirred for 36 h, filtered through Celite, and

evaporated to dryness. The oily deep red residue was extracted

with benzene and again filtered through Celite. The filtrate

was evaporated to dryness. The orange-red product 3 was

washed with cold pentane and dried in vacuo to give 258 mg

1

of 3 (93% yield). H NMR (CD₂Cl₂): δ -14.8 (w_1/2) 330 Hz,

PCH₃), -13.6 (PCH₂), -4.0 (w_1/2) 124 Hz, o-H), 0.4 (w_1/2) 45

Hz, p-H), 16.6 (w_1/2) 76 Hz, m-H). IR (KBr): ν 2008, 1975

cm^-1(CtC). The spectroscopic data agree well with the

literature values reported previously.¹⁶

F r om (MeC₅H₄)₂Mn , d m p e, a n d P h CtCH. The procedure

was analogous to that described above using (MeC₅H₄)₂Mn

(107 mg, 0.5 mmol), dmpe (150 mg, 1 mmol), and PhCtCH

(60 mg, 1.18 mmol) in 5 mL of benzene. Stirring for 20 h gave

269 mg of 3 (97% yield).

[(1,2-Bis(d im eth ylp h osp h in o)eth a n e)(η⁵-m eth ylcyclo-

p en ta d ien yl)(p h en yleth yn yl)m a n ga n ese(III)] Tetr a flu o-

r obor a te ([1a ](BF ₄)). To a cooled solution (-50 °C) of 1a (50

mg, 0.13 mmol) in 5 mL of dichloromethane was added a

solution of [(C₅H₅)₂Fe](BF₄) (35 mg, 0.13 mmol) in 2 mL of

dichloromethane. The mixture was stirred at -50 °C for 3 h.

Adding diethyl ether precipitated a red-brown solid which was

dissolved in dichloromethane and again precipitated with

diethyl ether (2×). The precipitate was washed with cold

diethyl ether (3 × 5 mL). Removal of the solvent gave 57 mg

of [1a ](BF₄) (93% yield) as a brownish powder. ¹H NMR (CD₂-

Cl₂, -20 °C): δ -70.5 (w_1/2) 246 Hz, o-H), -65.8 (w_1/2) 195

Hz, p-H), -52.4 (PCH₂), -46.3 (w_1/2) 1095 Hz, PCH₃), -20.4

F r om (MeC₅H₄)₂Mn , d m p e, a n d P h CtCSn Me₃. Stirring

a mixture of (MeC₅H₄)₂Mn (107 mg, 0.5 mmol), dmpe (150 mg,

1 mmol), and PhCtCSnMe₃(291 mg, 1.1 mmol) in 5 mL of

benzene for 70 h followed by workup as described above gave

250 mg of 3 (90% yield).

Bis(1,2-bis(d im eth ylp h osp h in o)eth a n e)bis((tr im eth yl-

silyl)eth yn yl)m a n ga n ese(II) (4). F r om (C₅H₅)₂Mn , d m p e,

a n d Me₃SiCtCH. A mixture of (C₅H₅)₂Mn (93 mg, 0.5 mmol),

dmpe (150 mg, 1 mmol), and Me₃SiCtCH (116 mg, 1.18 mmol)

in 20 mL of benzene was stirred for 14 h at 50 °C and then

cooled to room temperature, filtered through Celite, and

evaporated to dryness. The oily orange-red residue was

extracted with pentane and again filtered through Celite. After

the volume was reduced until the beginning of crystallization,

the solution was kept at -30 °C. A 247 mg amount of 4 (90%

yield) was collected as yellow crystals. ¹H NMR (CD₂Cl₂): δ

-14.9 (w_1/2) 256 Hz, PCH₃), -13.7 (PCH₂), 4.8 (w_1/2) 35 Hz,

Si(CH₃)₃). IR (KBr): ν 1942 cm^-1(CtC). The spectroscopic data

agree well with the literature values reported previously.¹⁶

(w_1/2) 663 Hz, C₅H₄), 42.4 (w_1/2) 257 Hz, m-H), 49.9 (w_1/2

)

541 Hz, CH₃C₅H₄). IR (KBr): ν 2070 cm^-1(CtC). FAB-MS:

m/z 385 (M⁺). Anal. Calcd for C₂₀H₂₈BF₄MnP₂: C, 50.88; H,

5.98. Found: C, 50.89; H, 5.65.

(1,2-Bis(d im et h ylp h osp h in o)et h a n e)(η⁵-m et h ylcyclo-

pen tadien yl)((tr im eth ylsilyl)eth yn yl)m an gan ese(III) Tet-

r a flu or obor a te ([2a ](BF ₄)). To a cooled solution (-50 °C) of

2a (25 mg, 0.07 mmol) in 3 mL of dichloromethane was added

a solution of [(C₅H₅)₂Fe](BF₄) (18 mg, 0.07 mmol) in 1 mL of

dichloromethane. The mixture was stirred at -50 °C for 3 h.

Adding diethyl ether precipitated an orange solid, which was

dissolved in dichloromethane and again precipitated with

diethyl ether (2×). The precipitate was washed with cold

F r om (MeC₅H₄)₂Mn , d m p e, a n d Me₃SiCtCH. The pro-

cedure was analogous to that described above using (MeC₅H₄)₂-

Mn (107 mg, 0.5 mmol), dmpe (150 mg, 1 mmol), and

Me₃SiCtCH (116 mg, 1.18 mmol) in 5 mL of benzene with

stirring for 7 h at 50 °C. Recrystallization of the crude product

from pentane gave 261 mg of 4 (95% yield).

Mono- and Bis(alkynyl) Mn(II) and Mn(III) Complexes

Organometallics, Vol. 18, No. 8, 1999 1539

F r om (MeC₅H₄)₂Mn , d m p e, a n d Me₃SiCtCSn Me₃. Stir-

ring a mixture of (MeC₅H₄)₂Mn (107 mg, 0.5 mmol), dmpe (150

mg, 1 mmol), and Me₃SiCtCSnMe₃(287 mg, 1.1 mmol) in 5

mL of benzene for 20 h at 65 °C followed by workup as

described above gave 253 mg of 4 (92% yield).

solution was stirred for additional 60 h. The volatiles were

removed under reduced pressure until a yellow-brown oily

residue was obtained. After extraction of the remaining oil with

pentane and filtration through Celite, crystallization at -80

°C gave 168 mg of 6 (43% yield) as orange-red crystals. The

mother liquor was evaporated, yielding an orange-red oil which

contained (MeC₅H₄)Mn(dmpe)dCdC(SiMe₃)SnBu₃as the main

product.

(1,2-Bis(d im et h ylp h osp h in o)et h a n e)(η⁵-m et h ylcyclo-

p en t a d ien yl)(p h en ylvin ylid en e)m a n ga n ese(I) (5) a n d

(1,2-bis(d im eth ylp h osp h in o)eth a n e)(η⁵-m eth ylcyclop en -

t a d ien yl)(p h en yl(t r ibu t ylt in )vin ylid en e)m a n ga n ese(I).

F r om (MeC₅H₄)₂Mn , d m p e, P h CtCH, a n d n -Bu ₃Sn H.

(MeC₅H₄)₂Mn (224 mg, 1.05 mmol) was dissolved in 5 mL of

benzene. To the resulting red solution was added dmpe (150

mg, 1 mmol). The reaction mixture turned pale yellow.

Phenylacetylene (102 mg, 1 mmol) was then added in one

portion. After the mixture was stirred for 20 h, n-Bu₃SnH (291

mg, 1 mmol) was added. After for additional 60 h of stirring

the volatiles were removed under reduced pressure until a red-

brown oily residue was obtained. After extraction of the

remaining oil with pentane and filtration through Celite,

crystallization at -35 °C gave 321 mg of 5 (83% yield) as brick

red crystals. The mother liquor was evaporated and dried in

vacuo, yielding a red-brown oil which contained (MeC₅H₄)Mn-

(dmpe)dCdC(Ph)SnBu₃as the main product.

6. ¹H NMR (C₆D₆): δ 0.31 (9H, s, Si(CH₃)₃), 0.85 (6H, vt,

J _PH) 3.7 Hz, PCH₃), 1.27 (6H, vt, J _PH) 4.4 Hz, PCH₃), 1.30,

1.69 (2H × 2, m, PCH₂), 2.06 (3H, s, C₅H₄CH₃), 3.87 (2H, m,

4

MeC₅H₄), 4.10 (1H, t, J _PH) 9.1 Hz, dC(H)SiMe₃), 4.26 (2H,

m, MeC₅H₄). ³¹P{¹H} NMR (C₆D₆): δ 93.2. ³¹P{¹H} NMR

(toluene-d₈): δ 95.1. ¹³C{¹H} NMR (toluene-d₈): δ 2.2 (s,

Si(CH₃)₃), 14.2 (s, C₅H₄CH₃), 21.8 (vt, J _PC) 5.3 Hz, PCH₃),

21.8 (vt, J _PC) 14.5 Hz, PCH₃), 30.8 (vt, J _PC) 21.8 Hz, PCH₂),

79.3, 83.8 (s, MeC₅H₄), 98.3 (s, ipso-C MeC₅H₄), 137.5 (s, d

C(H)SiMe₃), 339.3 (t, ²J _PC) 32.8 Hz, dCd). IR (KBr): ν 1583,

1558 cm^-1(CdC). EI-MS: m/z 382 (M⁺). Anal. Calcd for C₁₇H₃₃

-

MnP₂Si: C, 53.39; H, 8.70. Found: C, 53.80; H, 9.04.

(MeC₅H₄)Mn (dm pe)dCdC(SiMe₃)Sn Bu ₃. ¹H NMR (C₆D₆):

δ 2.12 (3H, s, C₅H₄CH₃), 3.80, 4.06 (2H × 2, m, MeC₅H₄). Other

signals were superimposed with those of 6 and free n-Bu₃SnH.

³¹P{¹H} NMR (C₆D₆): δ 92.8 (s). ¹¹⁹Sn{¹H} NMR (C₆D₆): δ

5. ¹H NMR (toluene-d₈, 10 °C): δ 0.74 (6H, vt, J _PH) 4.1

Hz, PCH₃), 1.11 (6H, vt, J _PH) 4.8 Hz, PCH₃), 1.12, 1.46 (2H

× 2, m, PCH₂), 1.94 (3H, s, C₅H₄CH₃), 3.86, 4.30 (2H × 2, m,

4

-23.7 (t, J _PSn) 74.6 Hz).

F r om 2a a n d (C₅Me₅)Mo(CO)₃H. 2a (42 mg, 0.11 mmol)

was dissolved in 3 mL of benzene. To the resulting orange-

red solution was added (C₅Me₅)Mo(CO)₃H (32 mg, 0.1 mmol)

as a solid in small portions. The reaction mixture was stirred

for 15 min. Removal of the volatiles under reduced pressure

gave a deep red oily residue, which was extracted with

pentane. Filtration of the solution through Celite, concentra-

tion, and crystallization at -80 °C gave 31 mg of 6 (80% yield)

as brick red crystals.

Oxid a tion of 6 to [2a ](BF ₄). To a cooled solution (-30 °C)

of 6 (69 mg, 0.18 mmol) in 5 mL of dichloromethane was added

a solution of [(C₅H₅)₂Fe](BF₄) (49 mg, 0.18 mmol) in 2 mL of

dichloromethane. The mixture was stirred at -30 °C for 2 h.

An orange solid was precipitated by adding diethyl ether. The

precipitate [2a ](BF₄) was collected and reprecipitated twice.

The precipitate was washed with cold diethyl ether (3 × 3 mL).

Removal of solvent gave 67 mg of [2a ]BF₄(79% yield) as an

orange powder.

4

C₅H₄CH₃), 5.82 (1H, t, J _PH) 8.7 Hz, dC(H)Ph), 6.83 (1H, m,

Ph H), 7.16 (2H, m, Ph H), 7.25 (2H, m, Ph H). ³¹P{¹H} NMR

(toluene-d₈, 10 °C): δ 92.8 (s). ³¹P{¹H} NMR (toluene-d₈, -98

°C): 93.1 (d, ²J _PP) 53.8 Hz), 94.5 (d, ²J _PP) 53.8 Hz). ¹³C{¹H}

NMR (toluene-d₈, 10 °C): δ 14.5 (s, C₅H₄CH₃), 21.2 (vt, J _PC

6.0 Hz, PCH₃), 23.3 (vt, J _PC) 14.9 Hz, PCH₃), 31. (vt, J _PC

)

21.7 Hz, PCH₂), 80.7, 84.6 (s, MeC₅H₄), 98.4 (s, ipso-C MeC₅H₄),

3

121.1, 121.7, 122.6 (s, Ph), 137.7 (s, ipso-C Ph), 142.2 (t, J _PC

2

) 5.2 Hz, C(H)Ph), 342.5 (t, J _PC) 35.5 Hz, dCd). IR (KBr):

ν 1594, 1564 cm^-1(CdC). EI-MS: m/z 386 (M⁺). Anal. Calcd

for C₂₀H₂₉MnP₂: C, 62.18; H, 7.57. Found: C, 61.99; H, 7.35.

(MeC₅H₄)Mn (d m p e)dCdC(P h )Sn Bu ₃. ¹H NMR (C₆D₆): δ

2.14 (3H, s, C₅H₄CH₃), 3.97, 4.39 (2H × 2, m, C₅H₄Me). Other

signals are superimposed with those of 5 and free n-Bu₃SnH.

³¹P{¹H} NMR (C₆D₆): δ 93.2 (s). ¹¹⁹Sn{¹H} NMR (C₆D₆): δ

4

-32.4 (t, J _PSn) 68.4 Hz).

F r om 1a a n d (C₅Me₅)Mo(CO)₃H. 1a (42 mg, 0.11 mmol)

was dissolved in 3 mL of benzene. To the resulting orange-

red solution was added (C₅Me₅)Mo(CO)₃H (32 mg, 0.1 mmol)

as a solid in small portions. The reaction mixture was stirred

for 15 min. Removal of the volatiles under reduced pressure

gave a deep red oily residue which was extracted with pentane.

Filtration of the solution through Celite, concentration, and

crystallization at -35 °C gave 34 mg of 5 (87% yield) as brick

red crystals.

Oxid a tion of 5 to [1a ](BF ₄). To a cooled solution (-30 °C)

of 5 (97 mg, 0.25 mmol) in 5 mL of dichloromethane was added

a solution of [(C₅H₅)₂Fe](BF₄) (68 mg, 0.25 mmol) in 2 mL of

dichloromethane. The mixture was stirred at -30 °C for 2 h.

A red-brown solid was precipitated by adding diethyl ether.

The precipitate was collected and reprecipitated twice. Ad-

ditionally the precipitate was washed with cold diethyl ether

(3 × 5 mL). Removal of the solvent gave 100 mg of [1a ](BF₄)

(85% yield) as a brownish powder.

(1,2-Bis(d im et h ylp h osp h in o)et h a n e)(η⁵-m et h ylcyclo-

pen tadien yl)((tr im eth ylsilyl)vin yliden e)m an gan ese(I) (6)

a n d (1,2-Bis(d im et h ylp h osp h in o)et h a n e)(η⁵-m et h ylcy-

clop en ta d ien yl)((tr im eth ylsilyl)(tr ibu tyltin )vin ylid en e)-

m a n ga n ese(I). F r om (MeC₅H₄)₂Mn , d m p e, Me₃SiCtCH,

a n d n -Bu ₃Sn H. (MeC₅H₄)₂Mn (234 mg, 1.1 mmol) was dis-

solved in 5 mL of benzene. To the resulting red solution was

added dmpe (150 mg, 1 mmol). The reaction mixture turned

pale yellow. (Trimethylsilyl)acetylene (100 mg, 1.02 mmol) was

added in one portion. After the mixture was stirred for 65 h,

tributyltin hydride (291 mg, 1 mmol) was added. The resulting

Bis[(1,2-bis(d im eth ylp h osp h in o)eth a n e)(η⁵-m eth ylcy-

clop en ta d ien yl)m a n ga n ese(I)](µ-2,3-d ip h en ylbu ta d ien -

1,4-diyliden e) (7).Fr om (MeC₅H₄)₂Mn ,dm pe,an d P h CtCH.

(MeC₅H₄)₂Mn (224 mg, 1.05 mmol) was dissolved in 5 mL of

benzene. To the resulting red solution was added dmpe (150

mg, 1 mmol). The reaction mixture turned pale yellow.

Phenylacetylene (102 mg, 1 mmol) was added in one portion.

After it was stirred for 6 weeks, the reaction mixture was

filtered through Celite. Volatiles were removed from the

filtrate under reduced pressure. The resulting red oily residue

was extracted with pentane (3 × 5 mL) until the extracts were

colorless. The red pentane extracts were collected and filtered

through a Celite pad. Partial removal of the solvent under

reduced pressure resulted in the initial crystallization of 7.

Additional cooling to -35 °C afforded 135 mg of 7 (35% yield)

as red crystals. The mother liquor contained a mixture of 3,

5, and 7. It was impossible to separate this mixture by

crystallization. ¹H NMR (toluene-d₈, 45 °C): δ 0.83 (6H, vt,

J _PH) 3.4 Hz, PCH₃), 1.27 (6H, vt, J _PH) 4.6 Hz, PCH₃), 1.15,

1.36 (2H × 2, m, PCH₂), 1.97 (3H, s, C₅H₄CH₃), 4.19, 4.29 (2H

× 2, m, MeC₅H₄), 6.76 (1H, m, Ph), 7.12 (2H, m, Ph), 7.37 (2H,

m, Ph). ³¹P{¹H} NMR (toluene-d₈, 45 °C): δ ) 95.7 (br). ³¹P{¹H}

NMR (toluene-d₈, -80 °C): δ 95.1 (d, ²J _PP) 42.6 Hz), 97.7 (d,

²J _PP) 42.6 Hz). ¹³C{¹H} NMR (C₆D₆, 21 °C): δ 15.6 (s,

C₅H₄CH₃), 22.2 (vt, J _PC) 5.8 Hz, PCH₃), 24.7 (vt, J _PC) 14.1

Hz, PCH₃), 31.3 (vt, J _PC) 24.0 Hz, PCH₂), 81.2, 83.9 (s,

MeC₅H₄), 97.7 (s, ipso-C MeC₅H₄), 120.9, 123.4, 128.3 (s, Ph),

4

3

130.6 (t, J _PC) 4.2 Hz, ipso-C Ph), 145.3 (t, J _PC) 4.2 Hz,

1540 Organometallics, Vol. 18, No. 8, 1999

Ta ble 5. Cr ysta l Da ta Collection a n d Refin em en t P a r a m eter s

Unseld et al.

2a

5

7

8

formula

color

cryst dimens (mm)

cryst syst

space group (No.)

a (Å)

b (Å)

c (Å)

R (deg)

â (deg)

γ (deg)

V (Å³)

Z

C

red

₁₇H₃₂MnP₂Si

C₂₀H₂₉MnP₂

red

C₄₂H₅₆Mn₂P₄‚C₆H₆

deep red

0.25 × 0.25 × 0.45

triclinic

P1h (2)

10.225(2)

13.887(2)

17.246(4)

106.37(2)

106.69(2)

96.53(2)

2199.5(7)

2

C₄₀H₅₆B₂F₈Mn₂P₄

red

0.47 × 0.30 × 0.05

triclinic

P1h (2)

8.632(2)

9.265(2)

14.544(3)

106.52(3)

100.23(3)

90.03(3)

1095.8(4)

1

0.75 × 0.65 × 0.5

monoclinic

P 2₁/c (14)

14.390(2)

11.180(2)

15.285(2)

0.3 × 0.3 × 0.3

orthorhombic

Pbca (61)

12.097(2)

15.543(3)

21.535(4)

116.30(1)

2204.5(6)

4

4049(1)

8

fw

381.40

1.149

0.792

386.33

1.267

0.808

848.72

1.281

0.750

896

944.22

1.431

0.785

488

d(calcd) (g cm^-3

)

abs coeff (mm^-1)

F(000)

812

1632

T (K)

203(5)

233(5)

5.0 < 2θ < 54.0

2.00-29.00

1.20

223(5)

296(2)

2θ scan range (deg)

scan speed (deg min^-1

scan range (ω) (deg)

no. of unique data

5.0 < 2θ < 60.0

2.00-29.00

1.20

5.0 < 2θ < 50.0

2.00-29.00

1.60

3.0 < 2θ < 56.0

1.70-16.50

1.00 + 0.35 tan θ

5277

)

6378

4263

7661

no. of data obsd (I > 2σ(I))

abs cor

soln method

R1, wR2 (%)^a

3861

none

direct methods

5.43, 15.5

1.051

3085

none

Patterson

11.3, 12.8

1.846

6289

none

direct methods

7.2, 13.6

1.231

3486

numerical

Patterson

5.68, 17.57

1.035

goodness of fit

R1 ) ∑(F_o- F_c)/∑F_o(I > 2σ(I)); wR2 ) {∑w(F²- F_c²)²/∑w(F_o²)²}^1/2

.

a

o

2

)C(Ph)), 342.6 (t, J _PC) 35.0 Hz, dCd); IR (KBr): ν 1589

(m), 1562 (m), 1518 (s), 1498 (s) (CdC), 931 cm^-1(m, P-C).

EI-MS: m/z 770 (M⁺). Anal. Calcd for C₄₀H₅₆Mn₂P₄: C, 62.34;

H, 7.32. Found: C, 62.46; H, 6.94.

Anal. Calcd for C₄₀H₅₆B₂F₈Mn₂P₄: C, 50.88; H, 5.98. Found:

C, 51.12; H, 6.29.

F r om [1a ](BF ₄). [1a](BF₄) (142 mg, 0.3 mmol) was dis-

solved in 5 mL of dichloromethane. The deep red solution was

stirred at room temperature for 6 weeks. Due to a high

decomposition rate insoluble products were formed. After

evaporation to dryness the oily black residue was extracted

with dichloromethane until the extracts were colorless. These

were filtered through Celite and concentrated. Crystallization

from dichloromethane at room temperature by slow evapora-

tion of the solvent gave 28 mg of 8 (20% yield) as orange

crystals.

F r om 8. 8 (47 mg, 0.05 mmol) was dissolved in 10 mL of

dichloromethane. To the resulting pale red solution was added

(MeC₅H₄)₂Co (21 mg, 0.1 mmol) as a solid. The reaction

mixture turned orange-red within 1 h. The reaction mixture

was filtered through Celite and evaporated to dryness. The

residue was extracted with pentane (3 × 3 mL) until the

extracts were colorless. The red pentane extracts were collected

and filtered through Celite. Slow evaporation of the solvent

at room temperature resulted in crystallization of 32 mg of 7

(82% yield) as red crystals.

Bis[(1,2-bis(d im eth ylp h osp h in o)eth a n e)(η⁵-m eth ylcy-

clop en ta d ien yl)m a n ga n ese(II¹/₂)](µ-2,3-d ip h en ylbu ta d i-

en e-1,4-d iylid en e) Tetr a flu or obor a te ([7](BF ₄)). F r om 7.

7 (38.5 mg, 0.05 mmol) was dissolved in 5 mL of dichloro-

methane. To the resulting orange-red solution was added

[(C₅H₅)₂Fe](BF₄) (13.6 mg, 0.05 mmol) in 2 mL of dichloro-

methane. The reaction mixture turned green-red within 30

min. The solvent was removed in vacuo, and the residue was

washed with diethyl ether to remove (C₅H₅)₂Fe. The crude

product was dissolved in 5 mL of dichloromethane, and the

solution was filtered through Celite. Addition of diethyl ether

caused precipitation of a green solid, which was again dissolved

in dichloromethane and precipitated with diethyl ether, giving

30 mg (70% yield) of [7](BF₄).

Bis[(1,2-bis(d im eth ylp h osp h in o)eth a n e)(η⁵-m eth ylcy-

clop en ta d ien yl)m a n ga n ese(III)](µ-2,3-d ip h en ylbu t-2-en -

1,4-d iylid yn e) Bis(tetr a flu or obor a te) (8). F r om 7. 7 (31

mg, 0.04 mmol) was dissolved in 3 mL of dichloromethane. To

the resulting orange-red solution was added [(C₅H₅)₂Fe](BF₄)

(22 mg, 0.08 mmol) as a solid. The reaction mixture turned

deep red within 15 min, and after 3 h it was pale red. The

reaction mixture was filtered through Celite. The filtrate was

concentrated by partial removal of the solvent to about half of

its volume. Addition of diethyl ether caused precipitation of

an orange solid. The crude product was collected, washed with

diethyl ether (3 × 2 mL) to remove (C₅H₅)₂Fe, and dried in

vacuo. Reprecipitation (2×) and crystallization from dichloro-

methane at room temperature by slow evaporation of the

solvent gave 36 mg of 8 (95% yield) as brilliant orange crystals.

¹H NMR (CD₃NO₂): δ 1.25 (6H, vt, J _PH) 5.0 Hz, PCH₃), 1.54

(6H, vt, J _PH) 5.9 Hz, PCH₃), 1.55, 2.00 (2H × 2, m, PCH₂),

2.01 (3H, s, C₅H₄CH₃), 4.16, 4.26 (2H × 2, m, MeC₅H₄), 7.50-

7.75 (5H, m, Ph). ³¹P{¹H} NMR (CD₃NO₂): δ 82.6. ¹³C{¹H}

NMR (CD₃NO₂): δ 15.2 (s, C₅H₄CH₃), 19.9 (vt, J _PC) 11.9 Hz,

PCH₃), 22.1 (vt, J _PC) 17.2 Hz, PCH₃), 31.5 (vt, J _PC) 21.4

Hz, PCH₂), 88.5, 94.0 (s, MeC₅H₄), 107.6 (s, ipso-C MeC₅H₄)),

131.3, 131.4, 131.6 (s, Ph), 134.7 (s, ipso-C Ph), 160.2 (s, d

C(Ph)), 307.50 (t, ²J _PC) 40.5 Hz, dCd). IR (KBr): ν 1632 (br),

1592 (w), 1576 (w), 1487 (m) (CdC), 1083 (s), 1055 (s, B-F),

931 cm^-1(m, P-C). ESI-MS: m/z 857 (M²⁺BF₄^-), 385 (M²⁺).

F r om 8. 8 (47.2 mg, 0.05 mmol) was dissolved in 5 mL of

dichloromethane. To the resulting light red solution was added

(MeC₅H₄)₂Co (11.0 mg, 0.05 mmol) in 2 mL of dichloromethane.

The reaction mixture turned green-red within 30 min. The

solvent was removed in vacuo, and the crude product was

dissolved in dichloromethane, filtered through Celite, and

crystallized at -30 °C, giving 17 mg (40% yield) of [7](BF₄).

EPR (CH₂Cl₂; -190 °C): g ) 2.018, A(⁵⁵Mn) ) 60 G. Near-IR

(CH₂Cl₂): λ 1018 nm (ꢀ ) 3.3 × 10³M^-1cm^-1).

X-r a y Str u ctu r a l An a lyses of 2a , 5, 7, a n d 8. The data

were collected on a Siemens P4 (2a ), Siemens P3 (5, 7), and

(63) (a) Sheldrick, G. M. SHELXS-86; University of Go¨ttingen,

Go¨ttingen, Germany, 1986. (b) Sheldrick, G. M. SHELXL-93; Univer-

sity of Go¨ttingen, Go¨ttingen, Germany, 1993.

Mono- and Bis(alkynyl) Mn(II) and Mn(III) Complexes

Organometallics, Vol. 18, No. 8, 1999 1541

Enraf-Nonius CAD-4 (8) diffractometers. Solution and refine-

ment were performed using the SHELXS-86 and SHELXL-93

software packages, respectively.⁶³Crystal data collection and

refinement parameters are given in Table 5. The rather poor

R values for the structure determination of 5 are due to the

lack of an absorption correction and the irregular shape of the

crystal.

Su p p or tin g In for m a tion Ava ila ble: Tables S1-S4, giv-

ing the DFT calculations, and additional material concerning

the X-ray structure analyses of the complexes 2a , 5, 7, and 8,

including complete listings of X-ray parameters, bond lengths

and angles, and positional and thermal parameters. This

material is available free of charge via the Internet at

http://pubs.acs.org.

Ack n ow led gm en t . We thank the Swiss National

Science Foundation for support of this work.

OM9810549

Article Doi

Versatile routes to mono- and bis(alkynyl) manganese(II) and manganese (III) complexes via manganocenes

DOI: 10.1021/om9810549

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