Transition Metal Hydrides - American Chemical Society

1 Relationships between Carbonyl Hydride Clusters and Interstitial Hydrides P. CHINI, G. LONGONI, S. MARTINENGO, and A. CERIOTTI

Downloaded by 185.14.192.192 on November 24, 2016 | http://pubs.acs.org Publication Date: June 1, 1978 | doi: 10.1021/ba-1978-0167.ch001

Istituto di Chimica Generale dell'Universitàe Centro del CNR, Via G. Venezian 21, 20133 Milano, Italy

Carbonyl hydride clusters based on small isolated polyhedra have not been found to contain interstitial hydride, whereas hydrogen atoms have been found to occupy partially the interstitial positions in clusters based on multihole polyhedra, such

as

n-

[Rh (CO) H ]

= 2,3).

13

24

5-n

n-

(n = 2,3,4) and [Ni (CO) H ] 12

21

4-n

(n

This behavior parallels that of simple metallic intersti-

tial hydrides and suggests a strong competition between metal-metal and metal-hydrogen bonds into the hole. For hydrogen, this competition is particularly severe because of the limiting conditions imposed by its orbital's s character, although interstitial hydrides are expected to be exceptionally stable in the presence of a high number of

µand µ ligands. 3

P

otentially, four metal atoms give rise to the simplest closed polyhedron, the tetrahedron, that could a c c o m m o d a t e a h y d r o g e n atom i n an interstitial position, and nearly 40 different examples of tetranuclear carbonyl hydride clusters are known (1, 2), as shown i n Table I. However, steric crowding between the c a r b o n y l groups w i l l prevent the f o r m a t i o n of a tetrahedron i n tetranuclear clusters containing 16 and 15 carbonyl groups (I), and open structures have been found b y x-ray analysis for [ R e ( C O ) i H ] " (3), [ R e ( C O ) i ] ~ (4), and R e O s 3 ( C O ) i 5 H (5). These open structures are also i n agreement w i t h the excess deviation f r o m the magic n u m b e r of 60 valence electrons. 4

5

4

2

4

6

2

W i t h 13 carbonyls, the metal atoms can adopt the usual tetrahedral a r rangement although considerable steric c r o w d i n g occurs w i t h the smallest metal atoms, as shown i n the short contacts present i n the d i a n i o n [ F e 4 ( C O ) i 3 ] ~ (6). (The shortest van der Waals contacts between the carbon atoms have been found experimentally to d e p e n d strongly on the relative inclination of the carbonyls: parallel carbonyls present a m i n i m u m distance of 3.0-3.1 A , w h i l e this distance decreases to 2.5-2.6 A at the relative angle of 9 0 ° - 1 1 0 ° ; this effect is clearly r e lated to the expected oval shape of the l i g a n d ( i ) . ) Cluster o p e n i n g occurs b y 2

0-8412-0390-3/78/33-167-001 / $05.00/0 ©

American Chemical Society

Bau; Transition Metal Hydrides Advances in Chemistry; American Chemical Society: Washington, DC, 1978.

TRANSITION M E T A L

2

T h e T e t r a n u c l e a r C a r b o n y l H y d r i d e s (1, 2)

T a b l e I.

[Re (CO) (OCH )H ]3Re Ru (CO)i H2 MnOs (CO) H ReOs (CO)i H [Re (CO) H pReOs (CO) H

(68)° (64) (64) (64)

[Re (CO) H ] MnOs (CO) H ReOs (CO) H Fe (CO) H Ru (CO) H Os (CO) H FeRu (CO)i H FeOs (CO) H FeRu Os(CO)i H FeRuOs (CO)i H [Fe (CO) H]" [Ru (CO) (RC R')H]

(60;T;4 ) (60) (60) (60) (60;T;2 ) (60) (60;T;2 ) (60) (60) (60) (62;) (60)

4

16

2

6

3

16

3

6

4

15

4

3

15

4

13

13

3

4

3

2

1 3

2

13

3

3

2

13

M

2

2

2

4

M

2

3

3

2

3

2

13

4

12

2

(64-4; lt + Zn)

(62;;lt) M

3

13

13

4

2

4

3


4

3

2

4

+

[Re (CO) H ] Re (CO) H Ru (CO)i H Ru (CO) _„L H Os (CO)i H FeRu (CO) H FeOs (CO) H [Ru (CO) H ]Co Os (CO)i H [Ir (CO) H ]2+ [Ir (CO) L H ]2+ FeCo (CO) H FeCo (CO) _ L H RuCo (CO)i H OsCo (CO) H [Fe Ni(CO) H]-

(60;T;6M) (56;T;4 ) (60) (60;-;4 ) (60) (60) (60) (60) (60) (60) (60) (60) W;T;ln )i> (60) (60) (60)

Ir (CO)„H [Ir (CO)„H]-

(60) (60;T;lt)

4

12

4

4

4

2

4

2

6

12

4

12

4

n

2

3

12

4

12

4

4

12

3

2

4

2

12

4

4

4

3

2

HYDRIDES

8

2

2

4

2

3

12

3

1 2

3

2

3

n

n

12

3

12

4

M3

6

M

3

2

4

(60;T;2t) (58) CO (T,-C H ) H (60;T;4 ) Ni ( ,-C H ) H (63;T;3M ) Number of valence electrons; cluster structure from x-ray, T = tetrahedron; number and type of H bonds. Neutron diffraction data. [Ir (CO) H ]2Os Pt (CO)8L H 4

10

2

2

4

4

2

2

5

J

5

5

5

4

2

4

4

M3

3

3

6

a

6

protonating [ F e ( C O ) i 3 ] ~ to give the monoanion [ F e ( C O ) i 3 H ] ~ , w h i c h adopts 4

2

4

a butterfly structure (7) (Figure 1). T h i s particular reaction indicates that there is no space for the i n c o m i n g proton either on the surface or i n the interior of the cluster, a n d it disproves previous claims that the h y d r o g e n was interstitial (8).


1.

Figure


Carbonyl Hydride Clusters and Interstial Hydrides

CHINI E T A L .

1.

Structural

change associated with [Fe (CO)is] protonation

dianion

2

4

3

S i m i l a r l y , the m u c h - d e b a t e d case of FeCo3(CO)i2H has been settled b y a l o w temperature

x-ray

diffraction

study

(9)

of

its d e r i v a t i v e ,

FeCo3-

( C O ) 9 [ P ( O M e ) 3 ] H , and has been confirmed recently b y neutron diffraction (10). 3

T h i s study shows that the hydrogen is u n d e r the basal plane. Whereas edge- a n d f a c e - b r i d g i n g h y d r o g e n atoms are associated m a i n l y w i t h m e t a l - m e t a l orbitals already present i n the tetrahedral skeleton (see last section) and therefore have limited steric requirements, terminal hydrides occupy a f u l l coordination position.

It is not surprising then that the only examples of

tetrahedral species w i t h t e r m i n a l hydrides contain 11 a n d 10 carbonyls, [ I r ( C O ) n H ] - and [ I r ( C O ) i o H ] ~ . 4

4

2

2

(The assignment for [ I r ( C O ) n H ] - is based 4

on the structure d e t e r m i n a t i o n of the analogous [ I r ( C O ) n B r ] ~ a n d o n the s i m 4

ilarity of the i r spectra of the t w o species (11).) P e n t a - a n d hexanuclear c a r b o n y l hydrides are m u c h less c o m m o n . T a b l e II.

Penta-, Hexa-, and Heptanuclear Carbonyl Hydrides

Carbonyl Hydride

Structure from X-ray

Os (CO) H [Os (CO) H]Ru (CO) H Os (CO) H [Ru (CO) H]-

trig, bipyr. trig, bipyr. octah. capped square p y r a m i d octah.

[Os (CO) H][Co (CO) H]-

octah. octah.(?)

[Rh (CO) H]Os (CO) (C)H

octah. capped trig, p r i s m

5

1 5

5

6

1 5

1 8

6

2

2

1 8

6

1 8

6

1 5

6

7

2

1 8

6

Only

1 9

2

M

H + M3(?) formyl type )r = - 6 . 5 )

Ref. 12 12 13 14 15

2M

a

14 16,17

M3

0- - - H - - -0 (r = -13.2) terminal n + term.(?)

c

1 5

Number and Type of H Bonds

6

16,18 19

Athough an interstitial position has been assigned to the [Ru6(CO)i8H)~ anion hydride (75), the experimental data are more compatible with a formyl situation. Hydrogen bonding to oxygen atoms in the [Co6(CO)i5H]~ anion is suspected because of extremely low field position of the signal (21)Based on the structure of the analogous [ R h ( C O ) i 5 l j " anol H N M R data. a

6

c

6

l


TRANSITION M E T A L HYDRIDES


4

Figure 2.

The hep structure

of the anions

[Rhis(CO) 4H - ] ~ 2

5 n

n

(n = 2,3,4)

nine different species (Table II) have been reported. A new situation where the h y d r i d e is associated w i t h one or more carbon atoms to give a f o r m y l situation (20) or w i t h hydrogen b o n d i n g to the oxygen atoms (21) is recognized readily from the particular low field position of the * H N M R absorptions. In these cases, deprotonation is facile i n L e w i s basic solvents and results i n loss of the H N M R signal because of exchange w i t h the solvent. Sometimes the ir spectrum i n solution can correspond to the deprotonated species. T h i s situation is probably more c o m m o n than the tables indicate. In the penta-, hexa-, and heptanuclear c a r b o n y l h y d r i d e clusters, t e r m i n a l hydrides are observed only i n the less c r o w d e d species, a n d again no evidence for the presence of interstitial h y d r i d e is found. O u r inability to observe interstitial h y d r i d e i n simple, isolated c a r b o n y l h y d r i d e polyhedra is i n contrast w i t h the situation i n larger multihole polyhedra. In the t w i n n e d cube-octahedron of [ R h i ( C O ) 2 4 H - „ ) " (n = 2,3,4) (22) i n Figure 2, * H N M R spectra show conclusively the interstitial nature of the hydride (23). In the distorted icosahedron of [ N i i ( C O ) 2 i H - „ ] ~ (n = 2,3), the same l

3

5

2

4

n

n


1.

Carbonyl Hydride Clusters and Interstial

CHINI E T A L .

5

Hydrides

conclusion has been reached more directly f r o m neutron d i f f r a c t i o n data (24). These five hydrides have a * H N M R signal i n the usual h i g h f i e l d region (28-39 τ), supporting our previous assignment of the low field signals reported i n T a b l e II.

In a l l these cases, the occupation of holes leads to a significant increase i n the

corresponding m e t a l - m e t a l distances, parallel to the general trend observed i n the simpler μ and μ hydrides (25, 26). 3


Features of Simple Metallic

"Interstitial"

Hydrides

T h e examples i n Table III, show that the hydrogen atoms occupy tetrahedral holes at the b e g i n n i n g of the transition series. As w e m o v e along the transition series, w e observe the interstitial h y d r i d e shift toward octahedral holes a n d the hydrides of the heavier elements become progressively unstable. P a l l a d i u m is exceptional since it is the only heavy element of group V I I I that gives a simple hydride. H y d r i d e f o r m a t i o n is accompanied i n most cases b y a change i n m e tallic lattice type and i n a l l cases b y a considerable increase i n m e t a l - m e t a l dis tances. T h e shift from tetrahedral to octahedral interstitial position is accompanied by a considerable increase i n the hydride atom's apparent dimension, w h i c h can indicate that the late transition metals are more electron r i c h a n d more prone to give u p a partial negative charge i n favor of the electronegative interstitial atom. T a b l e III.

Structural Features o f Representative Interstitial H y d r i d e s (27, 28) α

Ti hep 2.93

TiD Cr ccp bec 3.14 2.49 rH = 0.35 tet. AH ° = -29.6 kcal m o l HfD ccp 3.31 rH = 0.37 tet. AHf° = -33

CrH Ni ccp hep 2.49 2.71 rH = 0.55 oct.

1 9 7

6

6

fc

fc

NiHo.s ccp 2.64 rH = 0.55 oct. AH{° = -2.1 6

6

f

- 1

Hf hep 3.16

Pd ccp 2.75

1 6 3

6

6

La LaH hep X 2 ccp 3.742 4.019 rH = 0.51 tet. 2

6

c

6

LaH .92 ccp 3.973 tet. + oct. c

2

6

Ce hep 3.936

b

6

CeH ccp 3.958 rH = 0.46 tet. 2

b

6

CeH2.8o ccp 3.928 tet. -1- oct.

increasein R

increase i n R

~io ohm-cm

~io ohm-cm

6

Η positions based on neutron diffraction data. R) and 1 octah. hole (r + R = 1.414 R). Metal-metal distances, A. Η positions based on N M R data. α

PdHo.7 ccp 2.89 rH = 0.60 oct. AH{° = - 1 0

b

4

In cp structures: 2 tetrah. holes (r + R = 1.225

b

c


6


In a l l these cases, h y d r i d e f o r m a t i o n corresponds to partial occupation of the available holes, reminiscent of m u l t i h o l e p o l y h e d r a behavior.

Occupation

of a l l available holes w o u l d require a l i m i t i n g stoichiometry MH3, correspond to occupation of the unique hole i n isolated polyhedra. is k n o w n for some rare earth hydrides (see T a b l e III).

and would This situation

S i g n i f i c a n t l y , transfor-

m a t i o n of the m e t a l l i c d i h y d r i d e to the t r i h y d r i d e occurs w i t h a decrease i n a p parent m e t a l - m e t a l distances a n d w i t h a large increase i n resistivity.

These

observations indicate a salt-like character and the disappearance of m e t a l - m e t a l bonds (27). F i n a l l y , the heavier group V I I I transition metals' reluctance to f o r m stable interstitial hydrides c o u l d be related to the higher values of the m e t a l - m e t a l i n Downloaded by 185.14.192.192 on November 24, 2016 | http://pubs.acs.org Publication Date: June 1, 1978 | doi: 10.1021/ba-1978-0167.ch001

teractions (I ), as discussed i n the f o l l o w i n g section. Competition between Metal-Metal

and Metal-Hydrogen

Bonds

W e have shown that: A ) interstitial hydride formation is observed only w i t h partial occupation of the available holes, B) occupation of the interstitial position i n isolated p o l y h e d r a is not observed, a n d C) occupation of a l l the holes i n a close-packed lattice cancels m e t a l - m e t a l interactions. Therefore, it seems that interstitial h y d r o g e n can be tolerated only i n a fraction of the total n u m b e r of holes, a n d w i t h the w e a k e n i n g of m e t a l - m e t a l interactions. T h i s behavior i n dicates strong c o m p e t i t i o n between m e t a l - m e t a l a n d m e t a l - h y d r o g e n bonds, w h i c h is u n i q u e for h y d r o g e n because interstitial carbon c a n stabilize some u n usual arrangements i n c a r b o n y l carbide clusters (29, 30).

Table IV. Six metal atoms of the octahedron

Aig Aig Aig

s Pz

cU d

X 2

2

+

Px +

d

yz

Py

MO =

54

Topological correspond dence

Symmetry Relation .

+

center 8 faces 12 edges

+ Atom in the hole

s Px + Py + Pz d + d 2_ 2 djcy + d + d< 2

2

x

y

xz

9 AO =


*2g


1.

Carbonyl Hydride Clusters and Interstial Hydrides

CHINI E T A L .

6Z»« 1.414 R

( A )

Figure

3.

Representation

m

4.24 Z»e R

7

( Β )

of the metallic field in an octahedral (A) void and (B) filled

hole:

In a simple triangulated polyhedron, an octahedron for instance, electronic density distribution a m o n g the center, the triangular faces, a n d the edges is ex pected to be related to the n u m b e r a n d values of the C o u l o m b i c fields, F i g u r e 3A.

Introduction of an extra atom into the hole w o u l d give a new potential w e l l

( F i g u r e 3B) m a i n l y because the triangular a n d edge fields w o u l d change into

ships i n a n O c t a h e d r a l H o l e (Oh) Tl„

E E E

g g

Tlu

g

T2u

E

*2u

u

Tu Ti g

τ* τ* τ*

A 2u

+

Azu

Tig Tig

Eg Aiu

Tlu

+

Eg

+

2Tig

5T

l u

+

Tiu Tiu +

2T

l u

3T

2 u

Tiu +

Tiu

Tlu T-2g Eg

+

Tig

+

Ti

u


8



tetrahedral and triangular fields displaced towards the octahedron interior. A t the same time, the original central field w i l l increase because of the a d d i t i o n of the central positive nucleus, but its behavior i n the central region w i l l d e p e n d strongly on the electronic population of the added atones subshell. T h e result w i l l be a more homogeneous a n d localized f i e l d i n a new internal region where the added atom w i l l now interact w i t h most of the m e t a l - m e t a l bonds. As shown i n T a b l e I V , only 21 of the 54 M O s d e r i v e d f r o m the six metal atoms at the corners of an octahedron bear a topological correspondence (31 ) to the fields previously considered i n F i g u r e 3 A and therefore are expected to be most responsible for the m e t a l - m e t a l bonds system. A n extra central atom w i l l introduce, i n the intermediate region sketched i n F i g u r e 3 B , further limitations d e p e n d i n g on the s y m m e t r y of the available orbitals. H y d r o g e n is u n i q u e be cause the Is orbital can only m a t c h the A \ combinations; a l l the other M O s i n volved i n the metallic bonds w i l l become n o n b o n d i n g i n the region a r o u n d the octahedron center, and their electrostatic repulsion with the A \ electronic density w i l l decrease substantially the amount of m e t a l - m e t a l interactions. T h i s result can be proved by considering the s y m m e t r y products i n v o l v e d i n the electronic interactions (32). g

g

T h e insulator effect on m e t a l - m e t a l b o n d i n g for the interstitial h y d r o g e n atom i n an octahedral hole can be extended readily to other geometries. T a b l e V shows that a similar effect is expected i n a tetrahedral hole. T h e same effect could be i n v o l v e d i n the increase of the m e t a l - m e t a l dis tances observed i n the presence of μ a n d μ 3 hydrogen atoms (0.05-0.40 A) (25, 26) because i n C2 and C^ symmetries, only the A\ combinations are h y d r o gen-allowed. In these cases, however, geometric considerations indicate only partial disturbance of the m e t a l - m e t a l interactions. V

Table V .

v

S y m m e t r y Relationships i n a T e t r a h e d r a l H o l e (Tj) s

Four metal atoms of the tetrahedron

Ai Αχ Ai

Pz

d 2- 2 + Px + Py d + d x

xz

Topological correspondence

Ε Ε

yz

3Ai

center 4 faces 6 edges

Αι A\ Αι 3Ai

A t o m i n the hole

s d 2- 2 + d 2 d y 4- d + d Px + Py + Pz x

y

X

9 AO =

+

SE

+

6Τ

+

Ε

2 2 2

τ τ

Ε

+

2 2

2Τ

2

Αχ Ε

2

xz

3Τχ +

2

Ε

xy

36 M O =

Τι Τι Τι

2

2

d

y

τ τ τ τ τ τ

τ τ

2

y 2

2

A

1

+

Ε

+


2Τ

2

2

1. CHINI ET AL.

CarbonyI Hydride Clusters and Interstial Hydrides

9

The only authentic example of an interstitial hydride in an isolated poly hedron is the noncarbonyl cluster NbeliiH (33), better described by the formula [Νθ6(μ3-Ι)8Η](μ-Ι) /2. In the isomorphous Nbelii, eight iodides are face bridging over the eight octahedral faces, and each apex is occupied by an iodide common to two octahedra (34,35). In this compound, the eight μ$ iodides are expected to counteract the interstitial hydrogen atom since these face bridging iodides will distort the main metal-metal field outside the octahedron and make it much less sensitive to the interstitial hydride. This situation is reminiscent, for instance, of the contemporary presence of both a bridging carbonyl and a bridging hydride between the same metal atoms. In this sense, other exceptionally stable interstitial hydrides are expected in the presence of many μ or μ ligands. 6


3

Literature Cited 1. Chini, P., Heaton, B. T., "The Tetranuclear Carbonyl Clusters," Top. Curr. Chem. (1977) 71, 1. 2. Kaesz, H. D., "Hydrido Transition-Metal Cluster Complexes," Chem. Br. (1973) 9, 344. 3. Albano, V. G., Ciani, G., Freni, M., Romiti, P., J. Organomet. Chem. (1975) 96, 259. 4. Bau, B., Fontal, B., Kaesz, H. D., Churchill, M. R., J. Am. Chem. Soc. (1967) 89, 6374. 5. Churchill, M. R., ADV. CHEM. SER. (1978) 167, 36. 6. Doedens, J., Dahl, L. F., J. Am. Chem. Soc. (1966) 88, 4847. 7. Manassero, M., Sansoni, M., Longoni, G., J. Chem. Soc., Chem. Commun. (1976) 919. 8. Farmery, K., Kilner, M., Greatrex, R., Greenwood, Ν. N., J. Chem. Soc. A (1969) 2339. 9. Huie, B. T., Knobler, G. B., Kaesz, H. D., J. Chem. Soc., Chem. Commun. (1975) 684. 10. Koetzle, T. F., McMullan, R. K., Bau, R., Teller, R. G., Tipton, D. L., Wilson, R. D., ADV. CHEM. SER. (1978) 167, 61.

11. Giordano, G., Canziani, F., Martinengo, S., Albano, V. G., Ciani, G., Manassero, M., Chini, P., unpublished data. 12. Eady, C. R., Guy, J. J., Johnson, B. F. G., Lewis, J., Malatesta, M. C., Sheldrick, M., J. Chem. Soc., Chem. Commun. (1976) 807. 13. Churchill, M. R., Wormald, J.,J.Am. Chem. Soc. (1971) 93, 5670. 14. McPartlin, M., Eady, C. R., Johnson, B. F. G., Lewis, J., J. Chem. Soc., Chem. Com mun. (1976) 883. 15. Eady, C. R., Johnson, B. F. G., Lewis, J., Malatesta, M. C., Machin, P., McPartlin, Μ., J. Chem. Soc., Chem. Commun. (1976) 945. 16. Longoni, G., Martinengo, S., Chini, P., unpublished data. 17. Chini, P., J. Chem. Soc., Chem. Commun. (1967) 29. 18. Chini, P., Martinengo, S., Giordano, G., Gazz. Chim. Ital. (1972) 102, 330. 19. Eady, C. R., Johnson, B. F. G., Lewis, J., J. Chem. Soc., Dalton Trans. (1977) 838. 20. Casey, C. P., Neumann, S. M., J. Am. Chem. Soc. (1976) 98, 5395. 21. Mann, Β. E., personal communication. 22. Albano, V. G., Ceriotti, Α., Chini, P., Ciani, G., Martinengo, S., Anker, W. M., J. Chem. Soc., Chem. Commun. (1975) 859. 23. Martinengo, S., Heaton, B. T., Goodfellow, R. J., Chini, P., J. Chem. Soc., Chem. Commun. (1977) 39. 24. Dahl, L. F., Broach, R. W., Longoni, G., Chini, P., Schultz, A. J., Williams, J. M., ADV. CHEM. SER. (1978) 167, 93.


10

TRANSITION METAL HYDRIDES

25. Love, R. Α., Chin, H. B., Koetzle, T. F., Kirtley, S. W., Whittlesey, B. R., Bau, R., J. Am. Chem. Soc. (1976) 98, 4491. 26. Churchill, M. R., De Boer, B. G., Rottella, F. J., Inorg. Chem. (1976) 15, 1843. 27. Wells, A. F., "Structural Inorganic Chemistry," 4th ed., Clarendon, Oxford, 1975. 28. Mackay, Κ. M., "Hydrides" in "Comprehensive Inorganic Chemistry," Vol. 1, pg. 23, Pergamon, London, 1973. 29. Chini, P., Longoni, G., Albano, V. G., Adv. Organomet. Chem. (1976) 14, 285. 30. Albano, V. G., Chini, P., Ciani, G., Sansoni, M., Strumolo, D., Heaton, B. T., Mart inengo, S., J. Am. Chem. Soc. (1976) 98, 5027. 31. Kettle, S. F. Α., Theor. Chim. Acta (1965) 3, 211. 32. Fantucci, P., personal communication. 33. Simon, Α., Ζ. Anorg. Allg. Chem. (1967) 355, 311. 34. Bateman, L.R., Blount, J. F., Dahl, L. F., J. Am. Chem. Soc. (1966) 88, 1082. 35. Simon, Α., Schnering, H. G., Schafer, Η., Z. Anorg. Allg. Chem. (1967) 355, 295. Downloaded by 185.14.192.192 on November 24, 2016 | http://pubs.acs.org Publication Date: June 1, 1978 | doi: 10.1021/ba-1978-0167.ch001

RECEIVED July 19, 1977.


Transition Metal Hydrides - American Chemical Society

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