3  3,205,278  4  ing :atomic  numbers  greater  than 25  and less  than 29;  and of this  group, nickel  is  particularly  preferred.  The actual  chemical  structure  of the  catalyst  complex  of the  present  invention  is not  known.  the  hydrogenation  catalysts  may be  used as catalysts  over  a wide  range of  temperature,  such ,as,  for  example,  -10°  C. to as  high as  300°  C.  Preferably,  useful tem- peratures  are in the  range from  about ’20°  to 200°  C.  The 3-d  complex  metal salts  useful in  the  preparation  of the  hydrogenation  catalysts  must be  salts of  acidic  organic  compounds.  In  general,  salts of  organic  acids  having pKa  values  as  measured  in an ether  medium  at  25°  C.  in the range  1-20 are  satisfactory  metal salts  for  use in the  catalyst  preparation.  Preferably,  the acid  is  composed  of only  carbon,  hydrogen,  and oxygen,  and  contains  1 or 2  acidic hydrogen  atoms.  The  preferred  metal salts  are salts  of  monobasic,  strongly-acidic,  organic  acids having  pKa’s less  than 9.  In  general,  these acids  are  carboxylic  acids having  from  1-25 carbon  atoms per  molecule,  containing  only hydro› gen, carbon,  and oxygen.  By  monobasic  is  meant an  organic  acid having  only  one acidic  ,hydrogen  per  molecule  within the  pKa range  from 1-20.  Depending  upon which  metal salt  is  employed,  when  from about  ’2-5 moles  of a  trialkyl  or triaryl  Group  III  metal, for  example,  triethylaluminum  or  triphenyl-alu› minum,  are added  to one  formula  weight  of the  3-d  complex  metal salt,  a  highly active  hydrogenation  cata› lyst results.  A  chemical  reaction  takes place,  as gen› erally evidenced  by  evolution  of heat  of  reaction  and  the  formation  of  hydrocarbon  by-product.  Particularly  preferred  for  catalyst  preparation  are the  3-d  complex  metal salts  of  monobasic,  strongly-acidic,  organic  acids, the  salts of  which are  soluble  in  benzene  at 25 °  C. to some  appreciable  degree, i.e.,  of the order  of about  0.1  weight percent  and higher,  based on  ben› zene solvent.  In  general,  these metal  salts will  be those  of  organic  acids having  from about  6-25 carbon  atoms  per  molecule,  and these  limits can  vary in  some slight  degree,  depending  upon the  particular  metal cation  and  upon the  carbon structure  of the  hydrocarbon  skeleton  of the metal  salt anion.  Although  the  preparation  of the active  hydrogenation  catalyst  complexes  of the  present  invention  can be  ac› complished  by  mixing the  necessary  proportions  of es› sentially  anhydrous  finely divided  solid metal  salt and  organometallic  compound,  in the  presence  of an inert  atmosphere,  preferably,  catalyst  preparation  is  accom› plished  by  reaction  in the  presence  of an inert  liquid  diluent.  An inert  atmosphere  is one  substantially  free  of  oxygen,  water vapor,  :and other  compounds  known  to  be  reactive  toward  organometallics,  as well as  compounds  such as  amines,  ethers, etc.,  containing  atoms having  unshared  electron  pairs, such  as  oxygen.  Similarly,  :an  inert diluent  is one free  of  reactive  groups  (relative  to  the  organometallic  component  of the  catalyst)  and elec› tron-pair  donor atoms,  such as  oxygen.  Once  prepared,  the  hydrogenation  catalysts,  surprisingly,  appear  to suffer  no ill effects  from contact  with ethers,  ,alcohols,  ketones,  esters, amines,  nitriles,  and the  like, whereas  prior con› tacting  of the  organometallic  compound  and the  metal  salt in the  presence  of an ether,  such as  tetrahydrofuran,  does not  result in  the  production  of :active  hydrogenation  catalysts.  Of the 3-d  complex  metal  hydrogenation  catalysts  con› templated  in the  present  invention,  those catalysts  pre› pared by  the use  of  hydrocarbon  or  inert-medium  solu- ble nickel  salt are  most  preferred,  because  of  substantial  advantages  experienced  in their  use in  catalyst  prepara› tions and  because  of the  exceptionally  high unit  activity  of the  resulting  nickel  hydrogenation  catalyst  complexes  in the  hydrogenation  of  reducible  organic  compounds.  Thus, while  the  medium  insoluble  nickel salts  of  organic  acids upon  reaction  with the  required  amount  of the or› ganometallic  compound  generally  yield active  but par› tially  agglomerated  catalyst  complexes,  the  catalyst  ob› tained from  the  medium  soluble  nickel salts  are stable  complexes  of  extremely  fine  division,  generally  capable  of  remaining  dispersed  even in  ultra-high  centrifuge  force  fields, such  as one  generated  at  60,000 r.p.m.  for long  periods.  Inert diluents  useful in  catalyst  preparation  are, in  general,  hydrocarbons,  including  benzene,  toluene,  t-butyl› benzene,  white oils,  hydrocarbon  waxes, pentane,  heptane,  and olefins.  Where the  unsaturated  feed to  be hydro› genated  is a  hydrocarbon,  naturally  preparation  in situ  is  particularly  convenient  because  subsequent  purifica› tions, if  required,  are greatly  simplified.  Similarly,  where  an  unsaturated  hydrocarbon  diluent  is used  in  catalyst  preparation,  some  hydrogen  may be  consumed  in  saturat› ing  it,  but no  substantial  disadvantages  are  experienced.  Except  in their  use as  hydrogenation  catalysts  for the  !!"eduction  of  unsaturated  hydrocarbons,  preferably  ,and  advantageously,  the  catalyst  complexes  of the  present  invention  are  prepared  in  advance  of use in  an inert  dilu› ent.  The catalyst  components  react rapidly,  even at  moderate  :temperatures,  i.e., from  about  0°-100°  C., as  well as  at  reduced  and  elevated  temperatures,  i.e., from  about -50°  to about  200° C.,  and higher,  but below  the  well-known  thermal  decomposition  temperature  of  the 3-d  complex  metal salts  and the  organometallic  com› pounds.  In  general,  but with  some  relatively  minor vari› ation,  depending  upon the  nature  of the  material  to be  hydrogenated,  and the  particular  metal salt  employed,  Included  among  metal salts  of the  preferred  mono› basic,  strongly-acidic,  organic  acids are  the salts  of the  acids: formic,  acetic, propionic,  n-butyric,  isobutyric,  n- pentanoic,  isopentanoic,  hexanoic,  valeric, isovaleric,  ben,  Less desirble  than the  metal salts  of  strongly-acidic  organic  acids, but  nonetheless  useful for  hydrogenatio~  catalyst  preparation,  are the metal  salts of  weakly acidic,  organic  acids having  pKa values  in the range  from about  9-20, having  from 1-25  carbon atoms,  1-2 acidic  hydro› gen atoms,  and  containing  only carbon,  hydrogen,  and  oxygen.  Included  among the  weak acids  whose 3-d  com- plex metal  salts are  contemplated  for use  in  hydrogena› tion catalyst  preparation  are those  of the  carbinols,  such  as  methanol,  butanol,  hexyl alcohol,  2-ethylhexanol,  lauryl alcohol,  stearyl alcohol,  C$_{25}$H$_{51}$OH, octyl  alcohol,  cyclo hexanol,  octanol,  isobutanol,  eicosanol,  oleyl al- cohol,  octadecenol,  phenol,  lauryl phenols,  t-butyl phe› nols,  naphthols,  glycols,  n-C10H$_{21}$ CHOHCH$_{2}$ OH and  of  the  {3-diketones,  such as  acetylacetonate,  and higher  molecular  weight analogs  of  acetylacetonate,  and the  like,  The metal  salts of  weak organic  acids are  less  desirable  for a  number  of  reasons,  including,  in  general,  the rela› tive  difficulty  in  preparation  in the  required  essentially  anhydrous  salt form,  the  susceptibility  of most  of these  metal salts  to  hydrolysis,  a  tendency  to form  agglomer- ated  catalysts  of  somewhat  lesser unit  activity,  and the  like.  For the  preparation  of the  effective  hydrogenation  catalysts  of the  present  invention,  particular  amounts  of  organometallic  compound  must be  used for  each formula  weight  of the  3-d  complex  metal organic  acid salt.  Thus,  when less  than one  mole of  organometallic  compound,  for  example,  a  trialkylaluminum,  fa used  for each  formula  weight  of 3-d  complex  metal salt,  the  resulting  unit hy› drogenation  activity  of the  reaction  product  is  unsatis› factory.  Similarly,  when more  than about  6  moles of  the  organometallic  component  is used  for each  formula  weight  of the 3-d  complex  metal salt,  unit  hydrogenation  activity  is  substantially  lower than  the values  found for  the  prefer.red  ratios, namely,  from  about 2-5  moles of  an  organometallic  compound  per  formula  weight  of the  metal salt.  Although  some variation  ,is  noted, depending  upon the  particular  3-d  complex  element  salt being  used,  the  particula11ly  preferred  range  is  2.5-4.5  moles of  tri› alkylaluminum  per  formula  weight  of salt. 