use strict;
use warnings;
use Data::Dumper;

my @array = (
   'Schlüssel1    Wert1 Wert2',
   'Schlüssel2    Wert3',
   'Schlüssel3    Wert4 Wert5',
   'Schlüssel4    Wert6 Wert7',
);

my %hash;

foreach my $line (@array) {
   my ($key, @values) = split /\s+/, $line;
   $hash{$key} = \@values;
}

print Dumper(\%hash);