A global match and a split in a map.

$ perl -Mstrict -MData::Dumper -wle '
> my $string = q{{key_1 : value_1}{key_2 : value_2}{key_n : value_n}};
> my %hash = map split( m{\s*:\s*} ), 
>    $string =~ /{([^}]+)/g;
> print Data::Dumper->Dumpxs( [ \ %hash ], [ qw{ *hash } ] );'
%hash = (
          'key_1' => 'value_1',
          'key_2' => 'value_2',
          'key_n' => 'value_n'
        );
$
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