Bioinorganic Chemistry - ACS Publications

4 Developments in Inorganic Models of N Fixation Downloaded by UNIV OF CALIFORNIA SAN DIEGO on April 1, 2016 | http://pubs.acs.org Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0100.ch004

2

A. D. A L L E N Department of Chemistry, University of Toronto, Toronto 5, Canada This review covers most of the major developments reported during the past two years in the chemistry of stable transition metal-N compounds, emphasizing the nature of the N ligand and the remarkable range of compounds containing it, the wide variety of methods and reagents that lead to metal-N compounds, and the properties and reactions of these compounds. The position of the N stretching frequency of the bound N is a good indication of the extent to which the N molecule is modified by complexation, and possibly the extent to which it is activated toward further reaction. Known compounds in which N is bound simultaneously to two transition metals are increasing in number and variety. This development provides the most promising lead so far toward the link between these compounds and biological nitrogen fixation. 2

2

2

2

2

2

2

C i n c e this symposium includes authorities on many of the chemical ^ aspects of the fixation of nitrogen and its conversion to ammonia, this paper is restricted to a review of recent developments i n the preparation, properties, and reactions of N compounds of the transition metals, compounds that are stable enough to be isolated and characterized. The connection between these compounds and biological nitrogen fixation is uncertain at the moment. Most people assume that N is coordinated as such to a metal site at some stage i n the biological process, and that it is activated, at least partly, by this coordination. Unfortunately, despite early reports (1,2,3,4) to the contrary, no N compound that is stable enough to be isolated has yet been reduced, or induced to undergo any reaction that can lead to ammonia or a derivative of ammonia. There is, however, still good reason to believe that an interface between these inorganic systems and the biological systems does exist 2

2

2

79 Dessy et al.; Bioinorganic Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

80

BIOINORGANIC CHEMISTRY

and that we are slowly reaching the point where an understanding of the one w i l l help i n the understanding of the other. The recent flurry of activity i n this area by the inorganic chemists was started by the discovery at Toronto i n 1965 of the ruthenium com plex [ R u ( N H ) N ] X ( X — halide, B F " , PF [FeH(N )(depe) ]+ B P h " + N a C l acetone V N = 2090 c m "

4

2

2

4

1

2

it seems likely that the driving force is the removal of chloride ion as the insoluble sodium chloride and that N occupies the site left vacant by the departing ligand. The reaction (20) 2

C o H ( P P h ) + N [Ni(N )H(PEt ) ]

2

[Mo(acac) ]° + A l ( i B u ) + P P h

1

> [Co(N )(PPh ) ]°

Et 0 2

(23)

2

2

N

1

toluene

N 2

3

2

= 2065 c m "

> [Mo(N )(PPh ) (tol)]° 2

v

N 2

3

2

= 2005 c m "

1

(25)

Reducing agents vary from the mild amalgamated zinc i n aqueous solu tion to the strong aluminum alkyls. In their report of the preparation of [ C o ( N ) ( P P h ) ] , Speier and Marko emphasize the importance of using cobaltous acetylacetonate rather than the cobaltic complex used by pre vious workers (26). Ibers (27) points out that it seems unlikely that this would make any difference i n the presence of the very strong reducing agents used. This comment seems entirely justified, and it may be that the cobalt story is not yet fully told. W e now come to a number of reactions i n which reagents containing an — Ν — Ν — grouping, rather than molecular N , are used. In the prepa ration (12,13) of the rhenium compound, Figure 2, the benzoylhydrazine first acts as a chelate ligand, and on treatment with triphenylphosphine 2

3

3

2

L ReOCl L 3

2

+ PhCONHNH

L = PR , (R PCH ) 3

2

2

ÇI

\ I ^

N

R '

2

2

L

(

ReCl(N ) U 2

N

— —

^

— P h

'

L^ j^ N = t -

~

e

/

N—

COPh

Re

/1 L \ \L

+ PhC0 Me + HC1 2

CI

Figure 2.

Preparation of rhenium-N compound; data taken from Ref. 12 2

Dessy et al.; Bioinorganic Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

86

BIOINORGANIC CHEMISTRY (a) CI

CI

CO

:C—Ph

PPh . 3

Me0 CPh 2

MeOH/bz

+

I

PPh ^ J 3

y^t \

c

o

CO

CI

2105, 2020, 1930 cm-' , CHC1

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on April 1, 2016 | http://pubs.acs.org Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0100.ch004

(b)

3

PMe Ph 2

I

OC^

/.CO

N H

[Re(CO),(NH )(N.,)(PMe Ph) ]

2

2

v

N2

2

= 2225 cm-

2

1

PMe Ph 2

Figure 3.

Preparation of rhenium-N

2

compounds; data taken from Ref. 30

i n methanol an intermediate benzoylazo complex is produced. O n further reaction with the phosphine in methanol, this decomposes to give the product shown. Clearly, if this type of reaction could be reversed, many of our problems would be solved. The preparation of [ O s H ( N ) L ] ° mentioned earlier uses p-toluenesulfonyl azide as the reagent (14). 2

2

3

[OsH L ] + M e C H S 0 N - » [OsH (N )L ] 4

0

3

6

4

for L = P E t P h ,

2

v

2

3

N 2

2

2

= 2085 c m "

3

1

It is again assumed that the reagent acts first as a ligand which then decomposes in situ, leaving N bonded to the metal. Only a very few compounds have been prepared that contain more than one coordinated N molecule. Similarly, there are only one or two complexes known so far in which both N and C O are coordinated to the same metal site. Taube (28) prepared the first bis-nitrogen compound, c w - [ O s ( N H ) ( N ) ] , by the reaction of nitrous acid with [ O s ( N H ) N ] . Neither of these two o s m i u m - N compounds can be prepared using N as a reagent, but the carbonyl analogue of one of them, [ O s ( N H ) C O ] , has now been prepared (29) by the careful reduction of an osmium (III) complex with amalgamated zinc in the presence of carbon monoxide. Treatment of this compound with nitrous acid gives ris-[Os(NH ) CO ·N ] (29). T w o compounds of rhenium that contain one N and two C O groups have been reported, Figure 3. The preparation by Chatt et al. (30) uses benzoylhydrazine as a reagent in the presence of carbon monoxide; the preparation by Moelwyn-Hughes and Garner (31) uses hydrazine on a 2

2

2

n

n

3

5

2

3

4

2

2

2 +

2 +

2

2

n

3

2 +

5

3 4

2

2 +

2


4.

87

Models of Ν2 Fixation

ALLEN

compound that already contains the carbonyl groups. The band assigned to v i n the infrared spectrum of the second compound (2225 cm" ) is at a surprisingly high frequency, particularly when compared with Chart's results and bearing i n mind that substitution of N H ~ for CI" would be likely to decrease v rather than increase it. A possible explanation is that this is not an N compound at all, but rather an isocyanate. Further work is needed to clarify this point. 1

N2

2

N2

2

As soon as the first N complex was reported, many workers began looking for compounds of iron and molybdenum because of the biological importance of these metals. Compounds of iron were soon prepared, but it was not until this year that the first m o l y b d e n u m - N compounds were found. Misono et al have reported (25) the composition of the molyb denum complex mentioned earlier, together with the preparation of a second complex containing two molecules of N .


2

2

2

[Mo(acac) ]° + (diphos) + A l ( i B u ) + N -> [Mo(diphos) (N ) ] 3

3

v

2

2

= 2020(w), 1970(vs) c m "

N 2

2

2

0

1

F r o m the position and intensities of the infrared bands assigned to v > it is inferred that the product is the trans compound. N2

W e now come to a type of reaction for producing nitrogen com plexes that is important not only in itself but also because it indicates other possible routes back from coordinated nitrogen to a derivative of it. These reactions involve the reactions of a coordinated ligand that con tains the — Ν — Ν — grouping attached to the metal, using an external re agent that decomposes the ligand, leaving N on the metal. A n example (32) is 2

[ R u ( N H ) ( H 0 ) ] + + N 0 -> [ R u ( N H ) N 0 ] + + H 0 3

5

2

2

2

3

5

2

2

2

[ R u ( N H ) N 0 ] + + Cr +(aq) -> [ R u ( N H ) N ] + + Cr +(aq) 3

5

2

2

2

3

5

2

2

3

Armor and Taube also found (33) that if N-labelled N 0 is used, the resulting N complex slowly isomerizes to give a random distribution of N in the linearly coordinated N molecule. Since the rate of isomerization is rather faster than the rate of dissociation of N from the complex, they postulate an intra-molecular rearrangement involving a sideways-on 7r-bonded transition state 15

2

2

1 5

2

2

[ ( N H ) R u — N = N ] + 3

6

1 5

[(NH,)

2

6

( N H ) R u — ||| 3

5

Ru—ΝΞΞΞ Ν] + 15

2


88


This proposal is particularly interesting because no compound has yet been found to have this type of bonding, which is, of course, theoretically quite possible. One of the earliest reported reactions that led to the formation of m e t a l - N compounds was the decomposition of a metal azide. For ex ample, [ R u ( N H 3 ) 5 N ] slowly decomposes on standing at room tem perature to give [ R u ( N H 3 ) 5 N ] (2). Reaction of azide complexes with a variety of reagents has now been used successfully i n the prepa ration of N compounds. Basolo et al. (34) prepared the first ruthenium compound containing two coordinated N molecules by the reaction 2

l n

3

2 +


n

2

2 +

2

2

[ R u ( e n ) N · N ]+ + H N 0 ( a q ) -> [ R u ( e n ) n

2

2

3

n

2

(N ) ] + + N 0

2

2

2

2

2

V N = 2190, 2220 c m " 2

A similar reaction has been reported by Feltham et al.

1

(35).

[ R u ( d i a s ) C l · N ]° + NOPF (methanol) - * [ R u ( d i a s ) CI · N ]+ + n

2

3

n

6

N 0

2

2

V N = 2130 c m " 1

2

2

Basolo et al. have also reported (36) their investigations of the acidcatalyzed decomposition of coordinated azide. They find that the pri mary decomposition product is a protonated nitrene H I [ ( N H , ) , R u N ] + + H+ 3

3

3

5

2

Η

[(NH,), R u — Ν — Ν — Ν = Ν — R u ( N H ) ] 3

5

5 +

-> 2 [ ( Ν Η ) R u N ] + + Η + 3

5

2

2

and (b) by dimerization to give the N - b r i d g e d dimeric ion (to be dis cussed later). 2

2 [ ( N H ) R u N H ] + -> [ ( N H , ) , R u — Ν Ξ Ε Ν — R u ( N H ) , ] + + 2H+ 3

5

3

3

4

These reactions are very reminiscent of the behavior of organic azides when treated with acid or ultraviolet radiation, but there is little obvious chemical resemblance between the N - b r i d g e d complexes formed and organic azo compounds. 2


4.

Models of N

ALLEN

Reactions of Coordinated

89

Fixation

2

N

2

W e now come to the part of this story that has been most frustrating so far, but which is likely to be the area of greatest activity during the next year or two. Most attempts to induce the bound N molecule to react further have simply resulted i n the displacement of N by a new ligand. This type of reaction provides a useful synthetic route to a variety of compounds (2) but is of little interest to us at this time. There are four obvious ways in which the bound N might be attacked, by reduction, oxidation, photochemical excitation, and further coordination. A l l have been tried without success so far, but the results of these experiments are important for the information they give about coordinated N and for the possible indication they provide for future work. The use of strong reducing agents is illustrated by the work of Speier and Marko (37). 2


2

2

2

C o ( N ) ( P E t ) + n - B u L i -> Li+ [ C o ( N ) ( P E t ) ( P E t ) ] " + C H 2

v

N2

3

3

2

= 2059 c m -

[Co(N )(PPh ) 2

v

N2

3

3

v

1

N 2

2

2

6

= 2014 c m "

KPPh KPPh ç± [Co(N )(PPh ) (PPh )J*=± Phi Phi 2

3

2

= 2093 c m -

v

1

N 2

3

2

1 4

1

2

2

= 2016 c m "

1

[Co(N )(PPh )(PPh ) ] 2

VN

2

3

2

= 1904 c m -

1

2

2

Treatment of the cobalt nitrogen compound with n-butyllithium or potassium diphenylphosphide results in the cleavage of a phosphorus-carbon bond, leaving a phosphide, PR ~, as a ligand. The effect of the negatively charged, strongly ^-donating ligand is to reduce v substantially. It is remarkable that the c o b a l t - N linkage remains intact, even in the dianion, despite the great change in electron density on the metal. The v i n the dianion, at 1904 cm" , is one of the lowest frequencies so far reported and indicates a degree of activation of the N molecule that should be exploited, for example, by an attempt to coordinate the N to a second metal. Several workers have studied the oxidation of m e t a l - N compounds. Chatt et al. (38) found that oxidation of [ O s ( N H ) N ] with A g and C u ions in ethanol gave clear indications of an osmium ( I I I ) - N complex and the possible hint of an osmium ( I V ) - N complex. Page et al (39), using electrochemical techniques in aqueous solution, also obtained the osmium ( I I I ) - N complex but report that further oxidation leads to 2

N2

2

1

N2

2

2

2

3

5

2

2 +

2 +

+

2

2

2


90


decomposition, the rate of which is too fast for any osmium ( I V ) - N compound to be detected, even by rapid scan techniques. Electrochem ical oxidation of the osmium ( I I ) - N to the osmium ( I I I ) - N compound is a clean, one-electron, reversible process, the osmium ( I I I ) - N com pound decomposing to an osmium (III) aquo species at a first-order rate of 2 Χ 10" sec at 25°C. Similar experiments by Page et al. (39) with [ R u ( N H ) N ] show that it is oxidized irreversibly to give [ R u ( N H 3 ) O H ] . This shows that the ruthenium ( I I I ) - N com pound, if formed, is very much less stable than the osmium ( I I I ) - N analogue. Chatt et al. (38) have oxidized their robust rhenium (I) compound with metal ions and even with halogens without disturbing the m e t a l - N bond. 2

2

2

2

2

-1

n


i n

3

5

5

2

2 +

2

3 +

2

2

2

A g , Cu+ Fe + > [Re(diphos) CI · (N )]+ or X v = 2060 c m " H

[Re(diphos) CI · (N )] 2

v

N 2

2

= 1980 c m "

3

2

2

2

1

1

N 2

Since the ion [ R u ( N H ) 5 N ] has a strong electronic absorption bond at 222 nm, it is obvious that exposure to radiation of this frequency might produce interesting results. When this is done, Sigwart and Spence (40) report that a ruthenium (III) species is formed and gaseous nitrogen is evolved. A n important question, however, is the species reduced during the oxidation of ruthenium (II) to ruthenium ( I I I ) . In experiments with other ruthenium (II) compounds, F o r d et al. (41) find that H (from the solvent) is evolved, but Sigwart and Spence do not. It is just possible that some reduction of nitrogen occurs in their experiments, and work with N should be done to clarify this important point. Strangely enough, the one clear and well-documented reaction that does involve bound N was an early discovery by Harrison and Taube (42). n

3

2

2 +

2

1 5

2

2

[ R u ( N H ) N ] + + [ ( H 0 ) R u ( N H ) ] + τ± 3

5

2

2

2

3

5

2

[(NH ) Ru—N —Ru(NH ) ] + + H 0 3

5

2

3

5

4

2

The formation of dimeric N -bridged compounds still remains one of the most important discoveries in this field. The largest group of "dinners" of this type contain either two rutheniums or one ruthenium and one osmium. In addition to the above, the list of such compounds (29, 43) now in cludes: 2

{[(H 0) Ru] N } +,

{[(trien)Br · Ru] N } +

V N .= 2080 c m "

V N = 2060 c m " (vw)

2

2

5

2

2

4

1

2

2

2

2

1


4.

Models of Ν

ALLEN

91

Fixation

2

[(NH ) Ru—N —Os(NH ) ] , 3

5

2

3

4 +

5

V N = 2047 c m " (w) 1

2

[(H 0)(NH ) Ru—N —Os(NH ) ] , [(NH ) Ru—N —Os(NH ) CO] +, 2

3

v

4

2

3

4 +

5

3

5

= 2046 c m " (m)

v

1

N 2

2

3

= 2105 c m "

N 2

1

4

4

(m)


[(NH ) Ru—N —Os(NH ) ] +. 3

5

v

N 2

2

= 2034 c m "

3

5

5

(s)

1

In general, these compounds are prepared by the reaction of a meta l - N compound with a ruthenium (II) ion containing a replaceable aquo group. In the symmetrical { [ ( N H ) 5 R u ] 2 N } ion, v is at best very weakly infrared-active, but it appears in the Raman spectrum at about 2100 cm" (44), not greatly displaced from its frequency i n the par ent monomeric ion. The metal—Ν—Ν—metal group is essentially linear and the Ν—Ν bond distance (1.12A) is only slightly longer than that in free N (45). The mode of linkage of the ion [ O s ( N H ) ( N ) ( C O ) ] is through the N ligand rather than the carbon monoxide. This illustrates an important difference between the two, since no examples are known of an M—C—Ο—M bridge between two transition metals. The formation of such bridges between a transition and a nontransition metal, with the latter linked to the oxygen, has been reported recently (46). Presumably, the oxygen of the coordinated carbon monoxide is too π-electron rich to have much affinity for a transition metal ion containing nonbonding d-electrons. 2

4 +

2

3

N 2

1

2

3

4

2 +

2

2

It is clear that in these cases further coordination of the N does little to activate it. Our hope in studying these systems was that the unsymmetrical double coordination of N might lead to increased acti vation of it. W e were particularly interested in the fact that the [(NH ) Ru—N —Os(NH ) ] can be easily and reversibly oxidized to [ ( N H ) R u — N — O s ( N H ) ] . Page et al (39) have made an i n tensive study of the electrochemistry of these ions, and find the following. The { [ ( N H ) R u ] N } ion is reversibly oxidized (one faraday at >—€.5v with respect to a saturated calomel electrode) to an ion carrying a 5 + charge, which decomposes (fe = 10 Χ 10" sec' , 2 5 ° ) to [ ( N H ) R u N ] + [ ( N H ) R u ( O H ) ] . The [ ( N H ) R u — N — O s ( N H ) ] ion is reversibly oxidized (one faraday, at — O . l v ) to an ion carrying a 5 + charge, which is stable. Further oxidation at higher potential does not give a 6 + ion, but results in oxidative decomposition of the 5 + ion to [ ( N H ) O s N ] and [ ( N H ) R u ( O H ) ] . 2

2

3

5

2

3

3

5

4 +

5

2

3

5

3

2

2

5 +

5

4 +

2

2

2 +

3

3

5

2

3 +

5

3 +

2

3

5

1

3

2

5

3

2

3

5

5

4 +

3 +

Thus, it appears that there is little hope of sufficient activation of coordinated N in systems such as this, but this may be because the two 2


92


metals involved are not sufficiently different. More promising results along similar lines have recently been reported by Chatt etal. (47). They find that their rhenium complex reacts with a variety of early transition metal halides to give what appear to be deeply colored N - b r i d g e d com pounds with, in some cases, remarkably low N stretching frequencies. 2

2


Product V N + + + + L + Xs

[Re C l ( N ) ( P M e P h ) ] v = 1922 c m 2

2

4

1

N 2

Ti Cl,3THF Cr C l 3 T F H Mo C l 3THF Mo Cl 2Et 0 Mo Cl 2Et 0

1805 1890 1850 1795 1680

3

3

4

2

4

2

cm" cm" cm" cm" cm"

2

1 1 1 1 1

The authors confirm the v band assignments by N labelling, so that whether the actual structure involves an N bridge or not, the N bond has been considerably weakened in the product. They point out that only m e t a l - N compounds that already have v below about 1970 c m ' seem to react in this way; this excludes most of the known m e t a l - N com pounds but points clearly in the direction of work to be done. A n inter esting point here is the fact that the analogous [ R e C l ( C O ) ( P M e P h ) ] does not combine with these reagents. As pointed out earlier, the oxygen of bonded carbon monoxide has little affinity for other transition metal ions, apparently even including those from early in the transition series. 1 5

N2

2

2

2

1

N2

2

2

Polymeric N -Bridged

4

Compounds

2

Although it is possibly of little significance to our biological con siderations, the existence of stable, bifunctional, monomeric species leads to the obvious possibility of extensive copolymerization. As a first step on this road, Stevens at Toronto has prepared (29) what is almost certainly the first N -bridged trimeric ion, using the stable c i s - [ O s ( N H ) ( N ) ] as a starting material 2

3

4

2

2

2 +

0.1M H S 0 2

aV[Os(NH ) (N ) ] + + 2[(H 0)Ru(NH ) ] 3

4

2

2

2

2

3

5

2+

m-[(NH ) Ru—N —Os(NH ) —N —Ru(NH ) ] 3

5

2

3

4

2

3

6

6

4

•

+

This ion has A at 237 and 298 nm, and has one very weak N stretching frequency band at 2097 cm" . The presence of only one weak infrared band shows that both N groups are forming bridges and that the en vironment at each bridge is similar. Page and his group have made a preliminary electrochemical study (43) of this trimeric ion and find that it is oxidized (>0.8 faradays, + 0.44 ν ) to give [ ( N H ) ( N ) O s — N — R u ( N H ) ] + [ ( N H ) R u ( O H ) ] , and further oxidized (>0.8 faradays, + 0.65 ν ) to give m a x

2

1

2

3

2

4

2

2

3

5

4 +

3 +


3

5

4.

93

Models of Ν Fixation

ALLEN

2


[ O s ( N H ) ( N ) ] + [ ( N H ) R u O H ] . B y rapid cyclic voltammetry, they find that reversible oxidation of the 6 + trimeric ion to a 7 + trimeric ion does occur, but that oxidation of the 7 + ion is irreversible and results in decomposition. Work is presently i n hand using two bifunctional monomeric ions, [ O s ( N H ) ( N ) ] and [ R u ( N H ) ( H 0 ) ] , which possibly may lead to the formation of cyclic or long chain polymeric ions. 3

4

2

2

3

4

2

2

2 +

3

2 +

5

3 +

2

3

4

2

2 +

2

Summary The range of transition metal complexes containing the ligand N is now quite extensive and indicates the versatility of the nitrogen molecule as a ligand. Although no N compounds that are sufficiently stable to permit isolation have yet been shown to be capable of further reaction to produce ammonia, there is still hope that, by the simultaneous coordi nation of different metal ions onto the same N molecule, sufficient activa tion of the molecule w i l l be produced to enable a third reagent to break the nitrogen-nitrogen bond. If this is achieved, it w i l l help greatly i n our understanding of the biological process of nitrogen fixation. 2

2

2

Literature Cited (1) Allen, A. D., Senoff, C. V., Chem. Commun. (1965) 621. (2) Allen, A. D., Bottomley, F., Harris, R. O., Reinsalu, V. P., Senoff, C. V., J. Am. Chem. Soc. (1967) 89, 5595. (3) Allen, A. D., Bottomley, F., J. Am. Chem. Soc. (1969) 91, 1231. (4) Chatt, J., Richards, R. L., Chem. Commun. (1968) 1522. (5) Ahrland, S., Chatt, J., Davies, N. R., Quart. Rev. (London) (1958) 12, 265. (6) Temkin, M., Pyzhev, V., J. Phys. Chem. U.S.S.R. (1939) 13, 851. (7) Temkin, M., Pyzhev, V., Acta Physicochim. U.S.S.R. (1940) 12, 327. (8) Carra, S., Ugo, R., J. Catalysis (1969) 15, 435. (9) Allen, A. D., Bottomley, F., Accounts Chem. Res. (1968) 360. (10) Collman, J. P., Kubota, M., Vastine, F. D., Sun, J. Y., Kang, J. W., J. Am. Chem. Soc. (1968) 90, 5430. (11) Harrison, D. E., Taube, H., J. Am. Chem. Soc. (1967) 89, 5706. (12) Chatt, J., Dilworth, J. R., Leigh, G. J., Chem. Commun. (1969) 687. (13) Chatt, J., Dilworth, J. R., Leigh, G. J., Paske, R. J., in "Progress in Co ordination Chemistry," M. Cais, Ed., p. 246, Elsevier, Amsterdam, 1968. (14) Bell, B., Chatt, J., Leigh, G. J., Chem. Commun. (1970) 576. (15) Harris, R. O., private communication. (16) Sacco, Α., Aresta, M., Chem. Commun. (1968) 1223. (17) Knoth, W. H., J. Am. Chem. Soc. (1968) 90, 7172. (18) Creutz, C., Taube, H., private communication. (19) Bancroft, G. M., Mays, M. J., Prater, B. E., Chem. Commun. (1969) 585. (20) Speier, G., Marko, L., Inorg. Chim. Acta (1969) 126. (21) Davis, B. R., Payne, N. C., Ibers, J. Α., Inorg. Chem. (1969) 8, 2719. (22) Allen, A. D., Bottomley, F., Can. J. Chem. (1968) 46, 469. (23) Chatt, J., Leigh, G. J., Richards, R. L., Chem. Commun. (1969) 515.



94

BIOINORGANIC

CHEMISTRY

(24) Srivastava, S. C., Bigorgne, M., J. Organometal. Chem. (1969) 18, 30. (25) Hidai, M., Tominari, K., Uchida, Y., Misono, Α., Chem. Commun. (1969) 1392. (26) Yamamoto, Α., Kitazume, S., Pu, L. S., Ikeda, S., Chem. Commun. (1967) 79. (27) Ibers, J., oral communication. (28) Scheidegger, Η. Α., Armor, J. N., Taube, H., J. Am. Chem. Soc. (1968) 90, 3263. (29) Allen, A. D., Stevens, J. R., unpublished work. (30) Chatt, J., Dilworth, J. R., Leigh, G. J., J. Organometal. Chem. (1970) 21, 49. (31) Moelwyn-Hughes, J. T., Garner, A. W. B., Chem. Commun. (1969) 1309. (32) Armor, J. N., Taube, H., J. Am. Chem. Soc. (1969) 91, 6874. (33) Armor, J. N., Taube, H., J. Am. Chem. Soc. (1970) 92, 2560. (34) Kane-Maguire, L. A. P., Sheridan, P. S., Basolo, F., Pearson, R. G., J. Am. Chem. Soc. (1968) 90, 5295. (35) Douglas, P. G., Feltham, R. D., Metzger, H. G., Chem. Commun., in press. (36) Kane-Maguire, L. A. P., Basolo, F., Pearson, R. G., J. Am. Chem. Soc. (1969) 91, 4609. (37) Speier, G., Marko, L., J. Organometal. Chem. (1970) 21, 46. (38) Chatt, J., Dilworth, J. R., Gunz, H. P., Leigh, G. J., Sanders, J. R., Chem. Commun. (1970) 90. (39) Elson, C. M., Gulens, J., Itzkovitch, I. J., Page, J. Α., Chem. Commun., submitted for publication. (40) Sigwart, C., Spence, J. T., J. Am. Chem. Soc. (1969) 91, 3991. (41) Ford, P. C., Stuermer, D. H., McDonald, D. P., J. Am. Chem. Soc. (1969) 91, 6209. (42) Harrison, D. F., Weissberger, E., Taube, H., Science (1968) 159, 320. (43) Page, J. Α., et al., unpublished work. (44) Chatt, J., Nikolsky, A. B., Richards, R. L., Sanders, J. R., Chem. Com mun. (1969) 154. (45) Treitel, I. M., Flood, M. T., Marsh, R. E., Gray, H. B., J. Am. Chem. Soc. (1969) 91, 6512. (46) Kotz, J. C., Turnipseed, C. D., Chem. Commun. (1970) 41. (47) Chatt, J., Dilworth, J. R., Richards, R. L., Sanders, J. R., Nature (1969) 224, 1201. RECEIVED

June 26, 1970.


Bioinorganic Chemistry - ACS Publications

Recommend Documents